I wouldn't call Gouyoku Ibun a platformer. It's more like if you were to take one of the fighting games and then simplify literally everything about it. And frankly, I don't think it really works. The demo has a lot of problems. Unless the full version fixes those problems, I definitely don't think it will work as a starting point for new fans.
Personally, if someone wanted to get into Touhou but wasn't interested in the bullet hell games, I would probably recommend they start with ULiL and AoCF. The gameplay is honestly pretty simple as far as fighting games go, and the story and dialogue isn't random nonsense like in the early years of Touhou, making it less likely that they'll end up confused about what's going on. It also would help familiarise them with a good number of the more important characters.
Fortunately AoCF is likely being brought to the Switch, so hopefully it can serve as a decent entry point even without having ULiL set the scene first (despite being its own story, AoCF kinda just picks up where ULiL left off, so playing AoCF without playing ULiL first might be a little confusing). Ideally we need the Switch version of AoCF to have a recreation of ULiL's story mode to avoid that