Honestly, I've yet to see a character have significantly more survivability for having an 18 in their Prime Requisite. The last time I ran an AD&D game, I had a PC with an 18 strength, playing a Barbarian (also I am 99% sure in hindsight that they were cheating on their dice rolls). They still were the first PC to get killed.
One thing I've learned from running games for min-maxers is that when people do that, you hammer them on their weak points. Hit them with challenges using ability score checks in stats they've dumped. Good luck rolling a 6 or under on a d20.
It sounds like you'd do well surviving my games.
When playing a PC, the thing you should be asking is, "How is this character going to die?" and be mitigating against that. For example, it should cross your head in chargen, "What happens to this character if they fall into deep water?" If the answer is, "They drown", then that becomes a leading candidate for how the character will die. You should always be focused on avoiding the ways you can die and less on how you can get better at the thing you are already good at. Sure, being able to generate lots of damage reduces the chance of dying in combat, and that's great, but that's only one way to go out of the game. Sure, a great AC will help you survive combat, but if you insist on wearing heavy armor then you have to start looking at mitigating your issues real fast - you can't run away, you can't swim, you will slip and fall in rough terrain, etc. Not everything can be solved at chargen, but you should already be thinking about it.
That said, I do not deliberately try to hammer on any character's weak points. I don't want to let my bias influence outcomes. It's just I am a hiker and a caver and I let my setting be influenced by my real world experience, as well as my general simulationist outlook. You will fight on slopes, rough terrain, in water, in incliment weather, and so forth at some point. You will probably need to plan out how to run away as a party so as to not leave stragglers, because if you split the party people will die.
The optimizers tend to die because they optimize only for combat, thinking if they are a big enough hammer than can solve all their problems by hitting it hard enough. They aren't paranoid enough. They aren't creative enough, they don't cooperate well enough, and most of all they aren't thinking about, "How can I die?" except in terms of not winning a combat. I'm not intentionally hammering them, they are just optimizing for the wrong problem.
I haven't converted the Monk yet in these threads, and I've never allowed them in my games (except in my open table public games). One of the many many reasons for that is the class is optimized for leaving the rest of the party to die, and the players that play it tend to be asking the right questions ("How can I die?") but with a general solution being letting other characters die. If I do convert the Monk it will end up a very different class than the one people are familiar with.
That said, high stats especially in AD&D do make someone who is also a skilled player very hard to kill indeed.
