There is a mixture of stealth and aggression in most of the games. Usually the aggressive parts are forced on you in set play sequences and for the most part the rest can be done stealthily unless you mess up somewhere. The bosses can be taken out non-lethally if that counts as non-aggressive? Most bosses need some kind of stealth but sometimes its as little as just to break line of sight for an overkill ability.
You don’t like bosses in general or just the MGS ones? I enjoy the bosses but that’s probably because I beat them so many times as a kid. This bled into other games where I like boss battles in a lot of things now.
The recent Deus Ex games are quite similar, you played any of those?
As for the gameplay it is quite dated a far as mechanics go, did you try any of them when they released? Back then it didn’t seem so bad. MGSV is probably the most up to date in terms of gameplay but as a MGS game it sucked for a few reasons.