Where digimon and something called Gintana are more popular than cultural icons like Akira or masterpiece works of art like Sen to Chihiro no kamikakushi.

You're comparing the popularity of a show that actually aired on TV in many countries all over the world with an adult movie that released in 1988, a time where anime was still extremely niche in the west.

kizumongatari 3 and demon slayer really that much better than the anime of rhe past or have tastes simply changed?

It has nothing to do with "being better". More people watch anime now than in the past. And more people watch anime that comes out now than 30 year old anime.