You aren't playing summoner correctly, summoner is already ridiculously powerful in the right hands once you realize that the classes' gimmick is that you can stack damage of your own weapon on top of the damage your minions are doing... This isn't even mentioning the fact that the most broken build in the game is summoner. If anything summoner should be left alone for being the highest skill+highest reward class (In some cases it's actually lowest skill+highest reward). It straight up outclasses everything else. (using a massive stardust dragon+ phantasm decimates the moon lord...) It's also the only class that can use a Rod of Discord while attacking, though this isn't as powerful as the other point. To summarize, impure summoner is the way it's meant to be played, and Red even confirmed this.
By the way, I soloed four player expert mode moon lord potionless/nurseless with summoner and the build I used was so powerful it almost felt like cheating, so you can probably guess why I don't think it's underpowered.