The biggest differences I see are in speed. I don't go back as far as some of you but I bowled minor house tournaments not saying I was anywhere near high level good but I could keep it fun at least back in the early 80's. So I covered some plastic, a lot of urethane, and the beginning of resin was just coming out. Best average was 198 which made me at least competitive back then. Got married quit for 25 years just came back to the sport 4 years ago.
On my return I see people throwing 17 MPH and 20 MPH with pins rolling everywhere across the decks. Even with urethane the average bowler got up much above 15 mph the ball was a frozen rope and it hit terribly. No worries in the modern game chuck is as hard as you can and it still shapes up.
Unfortunately my ball speed is stuck 12.5 mph which was fine back then leads me to play extremely deep and with weak equipment compared to most. I struggle to stay in the low 190's and often score better with plastic than I do modern balls. Go to a tournament and see it takes 230+ to compete in the modern carry contest. I bowl leagues and have fun but I am not relevant in the modern game.
Probably unpopular opinion:
You're not irrelevant (using your words, no offense intended) in the modern game because of resin, you're irrelevant because you're not young anymore. I don't know you personally, but if you got married, quit for 25 years, and have been back 4, I'd guess you're closing in on 60?
I'm sorry you can't compete like you used to, that'll be a hard realization for me when the time comes. However, bowling is a sport. Athleticism SHOULD be required. If you can't physically get over 12.5mph, it's not the sport that's passed you by, it's your athleticism.
The ball/release match up to the lanes has to be much more perfect for the older guys than the younger guys, and while that's tough for older bowlers, it's still much more forgiving to age discrepancies than basically any other sport out there. I know some guys that age still competing at a very high level, hell just look at PDW. Those guys are exceptions, not the norm. Kudos to them.
I just don't understand the mindset that everyone SHOULD be able to compete. If that's the case, it's not a sport anymore, it's a bar game.
Btw, I don't get the impression you were complaining about not being able to compete anymore. Unfortunately, lots of people do, and I just happened to use your post as an example.