I know this has been covered many times, but I feel it needs to be said again.
Training grounds need an overhaul. Considering how outdated 3 and 4 star characters are, how can the easiest place to get characters give so little to the players? I’m sick of having two grounds at level 20 constantly doing ‘legendary’ training consistently churn out 3 stars. Two regions constantly training over a year for zero 5 stars. At least remove 3 stars from this or increase chances of 5 stars. I remember training grounds being the most exciting thing to upgrade when I was new to the game.
Another suggestion would be some form of trainer training. Make it 2 days if you must, and make it mostly Burts with a chance of rarer trainers too or even Liliths and Adens (might be a stretch because it would be too generous).
Anyway, enough of my rant… would just like to see something done there.