It sounds like you got the puppet ending, which is the worst ending and I fortunately never got. I know from reading the thread about that series that the way this HG was originally made, meant that it originally and unfortunately was quite easy to get that ending. And, that, I’d agree was a case of bad design. But the things that caused this were eventually fixed, not long afterwards, I think, and certainly long before I bought the HGs in that series, in 2021. If you tried that HG before this was fixed I fully understand your frustrations and am sad that you had to experience this. But after this was fixed, this became much easier to avoid. As far as I know the only way to get that ending is if you don’t escape as soon as possible in your one to one-encounters with the main villain before what is supposed to be the final battle and maybe also if you haven’t figured out the villain’s real/ original motivation and ask him a question based on what you’ve learned. The last thing is something I’ve never had any problem in doing, since that only involves succeeding in one stat check. But maybe you didn’t manage to that and this lead to your problems.
I won’t deny that some builds are more effective than others, but I don’t think this is necessarily a case of bad design. Firstly, there’s so many ways to build your MC in that series that even if some builds are less useful than others or even useless than others, there’s still many different builds you can use in order to win and I think that if you compare the number of builds that you can use to get a good ending in this series with the number of builds you can use in order to get a good ending in your average COG or HG, you will find that there’s at least as many builds you can use in order to that in this series, although that’s probably also partly to do with there being so many builds to choose from in this series in the first place.
Also, though it’s obviously not completely fair, making some stats more important than others, also helps signposting which stats to prioritise for the final confrontation. Considering the large number of stats for your character and the fact that there’s only so many of them you can choose from when you decide which of them you want to test, means, I think, that making them all equally important, will make it harder to figure out what the best choices are when it comes to what stats to build, which could quickly become a problem at the climax, when all the stat checks become extra important. It also makes it more difficult to remember for your next playthrough which stats that would be good to prioritise. Signalling that certain stats and builds are particulary good or bad, makes it easier for the average reader/player to figuring out a path into getting a good ending and can also function as a sort of easy mode or at least easier mode in a series that I don’t deny that often can be challenging.
Of course, if you have a preferred build that doesn’t work well and this build is the only build that you’re willing, this becomes difficult and I guess you’re then basically on hard mode or maybe even ultrahard mode. Which I get can be extremely frustrating. But I think for that for most people reading/playing a COG/HG or COG/HG series making all the stats of equal importance would make things more difficult or confusing, not least.
The thing to keep in mind is that is a very rpg-y HG series, at least in the tabletop rpg sense( I don’t feel that I have a good enough overview of computer rpgs to say anything about how similar it is to that kind of rpgs). And I’d say it’s particularly similar to rpgs like AD & D/D & D and (first edition)Pathfinder, all rpgs where your in-combat abilities; in this instance magic, melee, ranged combat and unarmed combat; are of prime importance, in the sense that you need to have at a high level compared to the challenges you face and ideally a secondary which you can use to supplement your best in-combat ability. And like in most versions of D & D/AD & D(and first edition Pathfinder), magic is the most useful abilty/stat. And like in many of the editions of those rpgs, some builds are better than others and some skills/abilities are better than others and part of the attraction for the people into this kind of playstyle is to create builds that are interesting and succesful/effective. And I think the combination of this and the series feeling challenging and the sense of accomplishment you get where you overcome those challenges through “building” your character and making good choices and end up getting the best ending or the other good ending, is at least an important part of what has made this series really enjoyable and attractive to many of the people who have really enjoyed that series.
So, although I can see that it feels unfair to you, and in some sense also is unfair, that certain builds are less useful, I still feel that to consider it bad design is taking it too far. I think there are reasons why it’s the way it is, and although this design has some unfortunate consequences, I think it has also has some good consequences and anyway is a part of the particular rpgy approach that this COG/HG uses. But it’s not for everyone, just like horror, shoot 'em ups, and even romance aren’t for everyone, so just like those who don’t like visual novels probably wouldn’t enjoy HGs that uses the same kind of approach, those who don’t like the approach of rpgs like D & D/AD & D probably wouldn’t enjoy The Lost Heir series either.
Anyway, I think a lot of what we like or don’t like in COGs and HGs has to do with our path into choicescript games. For me it was gamebooks, I literally discovered choicescript games through a web page about(mainly) gamebooks and played a lot of gamebooks when I was a young boy and, also has done so on and off, after becoming adult. The gamebook series I’ve played most often is the Fighting Fantasy series. In that series, you usually only had one good ending and plenty of bad ones and getting to the good ending usually took a lot of work, you both had to make the right decisions, find the right items, often had to solve one or more puzzles, and had to have enough luck with your dicerolls, both for combat rolls and stat checks in order to get that good ending and you very rarely got it right on the first attempt. You rolled up all your stats and there often wasn’t more build than hoping you would get high enough stats in the first place, which meant that it would become easier or more difficult depending on what stats you rolled. So compared to that, most HGs and COGs seem quite forgiving to me. This means that I’m probably less put off than the majority of other people who read play/read COGs/HGs when it comes to them being difficult and less forgiving of failure(although I do dislike when a COG/HG stops/freezes until you discovered the solution to a puzzle, puzzles were never really my favorite part of gamebooks and I’ve never really liked parser-based interactive fiction, partly for that reason). So you could probably say that my opinions, preferences and sensibilities, so to speak, are skewed towards being less bothered about those things in a COG/HG than the average COG/HG reader/player, but I think that kind of “skewing” happens to all of us one way or another, both by being less or more easily bothered by some things and by being more inclined to like particular approaches.
And it became such a staple of the genre that even stories that aren’t trying to be morality tales just assume that that’s the way time travel stories should be.