I can definitely see the frustration, but I'm curious if I'm understanding this right; would you want Sekiro to save progress in the middle of a boss-fight? If so that makes no sense to me. I've never played a game where I could go back to a boss after a death and have it at half health. That would take away the whole purpose of a boss fight in my view. You might as well be invincible since there's no need to learn the fight if you can start off right where you died previously.
For sure, but isn't this distinction completely arbitrary? They might as well remove the phases and keep a persistent health-bar throughout the whole fight and it would still be the same fight; it just wouldn't be as clear when you entered a new phase. The health bar is practically divided into three parts.
Well I finally got to sleep but nice to see some interesting discussion followed up! A lot of my points were kind of touched on already but I can respond to these directly too.
I did mention that games like Sekiro tend to vary in this - most of the actual boss fights (maybe all but 2?) in the game I was 100% fine with the actual fight. Most of the bosses don't significantly change between healthbar 1 and 2, and they only have the 2 to begin with. In those examples, any problem I have is with getting back to the boss fight itself, several of them just involve minutes of stealth clearing out adds before you get back to the fight (not challenging, not learning, just time wasted). Without spoiling it too much, the last boss in Sekiro is super duper the worst offender for me: The first phase is a huge nothing-burger, or at least seemed like it to me (it's literally a weaker version of something you fought earlier), but it still takes time to get through. The second phase is completely different, but the is still pretty manageable on the first try. The third phase is yet again VERY different, and a spike up in challenge but I somehow survived it, only to get to the fourth phase which is actually insanely boggingly hard and changes up the patterns AGAIN and is the actual thing I was stuck on. Because the phases are so different, going through them again doesn't actually help me get better at the phase I lose to, that's where my problem comes in. Bosses that just have the 2 bars are usually more or less the same across both and so it's not really the same issue I take with them.
That's why I use Furi as my highlight example: The first two phases are related and play on similar themes and tactics usually. The third phase of each boss may as well be an entirely different level, it's 100% different than the first two parts and you use 0 of the skills you use in the first two parts of each boss to get through it. It's a complete waste of time to keep redoing those first two phases when they have no bearing on the part that is a wall. As I mentioned, I was getting to that third phase on each new boss on my first try with all my resources intact, and then losing everything because it was so much harder and so different. There was literally nothing I could gain by redoing those first two phases again and again. That's more drastic than in say Sekiro but the principle to me is the same.
If the phases are so distinct and so different that it's reasonable to expect each phase to be a unique challenge, they should actually be separated by a checkpoint, or at least give players that option. In Sekiro, I even would have been fine with the final phase being checkpointed with my resources available as they were because flask charges were not the issue, dude was just slamming me because I couldn't read his attacks or figure out an opening. I just needed to practice literally that phase. Much like I wish in the multi-phase "boss" tracks in Thumper they let you checkpoint between the phases, because other rhythm games figured out that songs have very distinct segments and let you practice just those parts because maybe 95% of the song you can ace, but you die in that 5%, and redoing that 95% is meaningless at that point.
I do also have an issue where boss fights are too long for no reason, I actually prefer more lethal fights as long as your attacks are also lethal, and that actually helps mitigate some of the above issue. Most of the Sekiro fights were not especially long, and the ones that were stood out. A lot of games have fights that just feel like they overstay their welcome by like 20-40% to me, that's personal preference but it also sucks when you are good at the "challenge" and just twiddling through it because that's just how it is. Deadcells was notorious for this because all their bosses had severe damage caps so no matter what every fight lasted forever (I believe they recently changed that).
Again, I don't mind hard games or challenges that respect your time. I even beat all the stupid jerk Valkyries in God of War and those were completely unnecessary, but since you could just restart the fights almost instantly and they weren't "phased" really I just kept charging into them till I figured them each out.
Completely unrelated, but this looks like the first Humble Monthly I'll pause in over a year. I have Hitman 2 and Gris and Opus is the only game out of the rest I kind of want. Both Hitman 2 and Gris are good though, so not like I think the quality is bad, just kinda wrong assortment for me.