Guys PLAYED more physical because of the rules, some of them were heavier, they weren't generally stronger. As to the guys you mention... Luka is incredibly agile for his size, Jokic too, even Steph.. it's pretty telling that you picked 3 guys you think of as not great athletes, all of whom would be very good athletes in past eras... Luka is similar size to Larry Bird, he's much quicker and more agile, he jumps higher, he's stronger. Jokic weighs 30 pounds more than Patrick Ewing, and he's a more agile player, and not significantly worse (probably better honestly) in most other athletic categories. Guys have way better training regimines, they lift weights better, they eat better, they start specialized training earlier.The idea nba forwards were not stronger in the past shows you are either young or unaware. This group of nba guys went to the Olympics and complained it was too physical. That would have been impossible. This speaks to the reffing. The NBA does not allow the physical play of the past.
As I have said in the past the nba went too far with physical play. There are not Rodney Rodgers, Anthony Mason, Danny Fortson, etc. That there is no room for a guy whose greatest/only asset was bulk and strength is good, but today's players are not stronger.
I also laugh at young fans insisting everybody today is more athletic. Skilled yes. What Olympic events are Curry, Luka, Jokic winning? The game is more about skill, and that is awesome. At one time all 2s were like Westbrook, more athleticism than skill.
I watched plenty of late 80s and 90's games, you're mistaking athleticism vs. peer with pure athleticism... it's like comparing the 80s to Russell.. Bill Russel was the best athlete in the NBA by a good margin, he was an Olympian.... he wouldn't have been an Olympian in the 80s/90s and his level of athleticism would not have been the best in the league.
The NBA wings and guards of today are bigger, stronger, jump higher and are more agile than their 90s counterparts, this isn't even close. I'm not sure why this is controversial, we have TONs of evidence in every single sport, the Olympics, pre-draft testing, that over time athletes have significantly improved in every area.
Edit- I'd also note, the NBA was more "physical" in the past for several reasons:
1. Guys had less skill
2. Teams and players were dumb about the value of the 3pt shot
3. The rules were different
4. The league made less money so nobody cared what happened to those guys.