I concur. I've accepted this for the same reason you stated; their classic teams took a huge hit at the generation transition and they're still playing catch-up so I understand and support the things they've been working on fixing first (bringing faces up to speed, fixing jerseys, etc).
That said, improved classic atmosphere is near the top of my 2K wishlist because you're 100 percent right, the arena just feels fuller and more alive any time you play with current teams. To be more specific, here's some ideas off the top of my head:
1. Add the pregame national anthem to classic games (Bonus points: alter the singer's attire to reflect the era of the home team playing)
2. Add pregame starting lineup introductions to classic games. (Bonus points: implement some signature tidbits from the most memorable classic lineup introductions, similar to 2K11's "Sirius" Michael Jordan intro, or maybe just adding a "B-B-B-B-Ben Wwwwallace" to the background of a generic 2004 Pistons starting lineup). ((Super Bonus Points: Bring back the 2004 Pistons' flames behind the buckets during their intros)).
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3. Custom classic arena sounds. I believe this was a feature in previous 2K's (around 2K12). Since then, I believe a lot of those custom arena sounds have given way to a lot of generic classic arena sounds (like a "Charge" tune).
Moreover, with so many 90's and 80's songs on the soundtrack this year I thought there was an outside shot they'd play a specific role when it came to classic arenas. As in, I thought maybe "I Can't Drive 55" would be more likely to play at the '87 Great Western Forum than, say, Anderson Paak. I'm not sure that's true though. It'd be nice to at least have the option to edit and/or add sounds for classic arenas (again, another former 2K feature no longer available).
4. Yes, I know, it's been beaten to death but honestly... bringing back optional era filters would help bring some of these games to life.
5. Filling out the sidelines: This means things like...
A. Going the extra mile and finally outfitting retro teams in their authentic warmups
B. Adding more cameramen to the baseline
C. Eliminating strange gaps in classic arenas, usually near the corners of the floor that lead off to dark, vacuous lockerroom walkways
D. Lightening up the arenas. A lot of modern arenas have blacked out their crowds a little. Most classic arenas did not do this. Could be a placebo because I'm enjoying playing 2K18 so much but a number of the classics don't feel as dark as they did last year but maybe it's because I'm using more modern classic teams that didn't have that issue.


6. Coach Editing Feature/Create-a-Coach: Obviously, classic teams are going to miss out on things like post-quarter interviews (in-studio, sideline, in-the-huddle coach instructions) all aren't going to work with classic teams for obvious reasons. However, allowing gamers to at least choose who roams the sidelines for those classic teams would be a big step in the right direction, even if the create-a system were a bit crude. Just about anything would be an improvement over this:

Even if create-a-Phil Jackson looked like this...

It'd still be better than what we've got.
7. General arena ambiance: Beyond signature sounds, just a fuller feel from the crowd itself would really bring those classic games together. That also goes for non-classic games though.
8. Player graphics and wipes that represent their specific season. This might be in but I'm going to mention it just in case it's not. I have a feeling that at certain points the classic player graphics show 0.0 stats instead of their stats for their given year but I could be totally wrong about that. Bonus points: have the crew allude to storylines from that particular year being used. The game has some good classic player references but obviously, they haven't come close to touching 2K11 and 2K12 (the former setting the bar by going as far as to mention Michael Jordan's real life weightlifting injury that occurred prior to one of the Jordan Challenge games).
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