Obviously it has to be within reason, I played Super Meat Boy for about 100 hours or so and 100%'d and got all ironmans so I can say that it is a very poorly designed game, but it just really becomes exhausting at a point, as even that was really excessive and there was no satisfaction. It's more about at least experiencing everything it has to offer or seeing the new prospective or gameplay change from increased difficulty. With something that is designed to be a time sink where you just recite the pattern for hundreds of hours, a small sample of that is plenty.
Also, I have mastered many shmups, just obviously not at the level of people who have spent 10-50x as long as me playing. And I'm not going to sink hundreds of hours many times over into each bullet hell clone pumped out just because each one has a gimmick and a reskin.
I would be near the end of the Dunning Kruger Effect since I have extensive experience within the field. I have actually felt this effect, where you just feel a bit hopeless; there is just literally not enough fucking hours in the day to dedicate. You spend time to be good at x, and then you spend all your time on x, but the guy who spent all his time on y is better than you at y. Some of these people just dedicate every fucking waking hour to this shit, but I only do it as a hobby and I like to have my life be balanced in other respects.
Again, I just want to reiterate, that you only view bullet hells as deep or strategic because they rely on the crutch of insane difficulty and muscle memory to make up for their shallow, derivative, and simplistic gameplay. Pretty much any game can not only be made much more "complex" but well beyond the realms of human ability just through a few simple changes or alterations to mechanics or addition of a very gradient scoring system. But vast majority of people don't find that fucking enjoyable or satisfying, it's just grating as hell and makes you reconsider your life.