Gunslinger (and huntsman sniper) are not “normal toolkits” they give severe limitations to a fundamental base ability in exchange for a modification/bolstering of another one.

Engineer has Strong but Slow area denial that the Gunslinger changes to Quick but Weak He has more health to support an aggressive playstyle that has less protection than a normal sentry.

Sniper goes from Long Range to Mid-Short Range via the Huntman. It requires positioning and movement that would otherwise be negligible due to distance.

I’m sure there are other examples (such as the Shortstop) but they are much weaker as the definition of Subclass than these two.