by Gewar
My 2 cents:- diminishin channeling when damaged is mechanism that punnishes player who already is loosnig - it will surely reduce time of typical play, but it will cause running away leader effect, which is, in generall, not welcome in most board games.
- perfect counter issue happens mostly when you have only one oponent - you can't make spellbook that counters everything unless it is everything you are focusing on - and you should focus on killing your oponent too. Maybe it is main reason, why your plays are so long - counter decks and healing decks in cardgames are ussually slowing down enemies -> making game longer. Try Beastmaster swarm or big-pet, Wizard lightning, Priestess archery or Warlock anything - focus on attacking and see, how your oppnent try counter all spells, but there are just too many of them.