Er, whoa R38. I get that dating is frustrating (for everyone - think of what straight women in their 30's experience if they want to start a family), but I actually don't think things are that bleak.
First - why the assumption that all gay men want to be with some fit ideal who looks just like them (if they themselves are fit)? A lot of gay men aren't looking for a clone of themselves, and are actually turned on by difference. The most basic, crude example is tops and bottoms, but it applies to older guys into younger guys and vice-versa, more muscular guys into twinks, etc. I consider myself to be pretty fit and slender, but honestly I like guys with a bit more bulk to them and don't mind a few extra pounds - gives me more to hold onto :) So don't assume if you see two guys together of different body types that one of them "settled" for someone less than ideal, or assume that all gay men are attracted to the same thing.
Actually, one of the most refreshing things I learned (if you can call it that) was from going on a hookup app, Jack'd, which has a feature that lets you see stats on which profiles a particular guy showed interest in - average height, weight, race, etc. And I was surprised by the diversity that was revealed - some guys who looked like classic WASPs were really into short Latinos, or a tall gym-rat was really into heavier guys, etc. Everyone has their own particular attractions for who knows what reasons.
And the most important point - never, ever confuse dating sites or hookup apps with the entirety of the "real world". They are a small subset of the world. I have run into a few gay men I know in real life on them, but the majority I have not. Most of the gay men I know I met through things like school, or parties, or activities, or friends of friends, etc. Just because you strike out or have a bad run on dating apps does not mean there aren't still plenty of available men out there, but you do have to get out to meet them in person.
And online interactions are always going to be more shallow, dehumanizing, and even misleading than encountering people in real life. I've met guys who looked amazing online who weren't all that in person, and vice versa. One of the guys I dated first messaged me on OKCupid, but then stopped responding after a message or two. I forgot about him, but later we met in person by chance, through friends of friends, and he couldn't ask me out quickly enough. Same with another guy who only glanced at my profile online, but when I ran into him at a party asked for my number then and there. OKCupid and other sites are good for supplementing your social life to meet people you might not run into (and for providing extra info you might not learn early on - "ugh, that cute guy's a rabid right-winger!"), but you should still live your life and get out there.
I mean, I still think your advice is good - keep your expectations in check, don't always prejudge others or assume you're not a match because of your preconceived notions of who you're meant to be with, and be open to stretching yourself and meeting people you might not otherwise meet - you might be pleasantly surprised. But also don't think you have to "settle" for someone you just don't feel any attraction to because you think the world is limited to a dating site and there's no one else available, and end up meeting people you have no real interest in - it's a waste of everyone's time, and honestly they deserve better.