If Thor had gone up to Thanos and just zapped him dead effortlessly with a single blast, that would've felt like a cheat too.
Edited to add: Thinking about it a bit further, I guess it feels different because Stormbreaker was a brand new toy, so we had nothing to compare its power level against, and we'd seen Thor go through extraordinary lengths to acquire it, so the story had carefully built a sense that this new hammer was A Really Big Deal. But in this episode, it's just Vision's body, a known quantity with a power level well-established across the various films.