As someone who has recently become somewhat fatigued with seemingly non-stop matches against NG mill and MO relict decks, both in ranked and training mode, I had a recent thought that might prevent players from getting frustrated against continually matching against their least favourite match ups.
What if the game let you pick the factions you wanted to play against in training mode PvP? The game could then match you against someone who has selected your faction on the training mode list. I think this could prevent people from getting frustrated playing continually against hated match ups, or let people try their decks against particular factions to improve their knowledge and skill of how they play against one another.
Obviously this would only work in training mode and it would probably be best if you couldn't veto the faction you were currently playing as, but it might be a good way of breaking player frustration and tilting, as well as fatigue at encountering the same couple of strongest decks.
Appreciate that this is probably quite complex I'm terms of matchmaking technology, but I think if it were possible, I would happily take longer matchmaking times to play against specific factions and avoid others.