Taining grounds is not a place where you can test and improve your decks because if you make a deck for an event the opponent you get is random, could be standard or not, any color, any planeswalker…
Should not be an event, just somewhere to play as much as hou want without any rewards (of course if you take back Quick Battle, there shoud be always a place to get runes to improve planeswalkers).
Training grounds could be a good option if player could choose:
-Opponent planeswalker decks (Koth deck, Dovin deck, Saheel deck…)
-Opponent from events (for example planeswalker in node 3.1 od Trial of Zeal)
-Decks that fulfill the standard rules in each moment
-Decks from a selected player
-Own player decks
This could be the perfect tool for anyone to improve .