Some of these might qualify as Divinity 2 ("I wish this was in the game"), but...
1) Summon Mastery should also increase the number of summons you can have out at once. One summon at Rank 1 and 2, two summons at Rank 3 and 4, three summons at rank 5 (or two summons at rank 2 and 3 and three at rank 4 and 5). That would make a summoner build more useful.
I don't want to get off subject here, but you bring up an interesting point. It makes me wonder if that could be something to include in a future patch. It seems like it might be easy to adjust the cancellation triggers, but I'm just a gamer and not a programmer.
Food for thought...
