At the highest levels, my best guess is on average they've gone down. Compulsories in my area have gotten a lot more competitive since the 90s though. In level 4 I did 2 hour practices twice a week, and halfway through a third two hour practice become available. I got a kip, back tuck, and back walkover on beam doing those hours. But we did much less work on routines and the routines were more straightforward. Now level 4s usually practice 9-12 hours a week, and level 5s practice 12 to 16 hours.
But at the same time, upper levels were the same or even more...crazier practices. I'm talking about specifically my area. My older cousin was around a level 9 at the time I was starting gymnastics and they were doing two practices a day (one before school). Don't know of any gym in my state that does that nowadays for a JO track level 9 or 10 (i.e. a gymnast who does not plan to be elite and isn't homeschooled).
Edit: the compulsory routines had really similar skills, but the choreography was a lot more straightforward (the hardest dance move was a backward chasse, generally terribly executed). A lot of gyms didn't compete level 4, and the level 5 routine was definitely much easier (same skills - FHS, 2 BHS, back extension, straddle jump). The quality of performance was much lower at these levels in general. Now the kids have to be very polished to compete.
