I do think the 350 is more effective than the 30-30. I also think the 30-30 is fine for deer but it’s the absolute least powerful cartridge I would be willing to use. I’m normally a magnum guy but I do prefer the 350 to a slug gun, I bought it when Iowa became a straight walled state and before they removed case length and shouldered restrictions and I’ve just seen too many deer drop to it to consider the 350 underpowered.
My non Iowa deer gun is a 257 weatherby magnum, and until I sold it my elk gun was a 30-378 weatherby, so I definitely prefer more, but I’ve seen too many deer drop to the 350 to argue that it’s not powerful enough. Its mild recoil and quiet (relatively speaking) noise means pretty much anyone can shoot it accurately. I think I’d trust the 350 legend more than I’d trust a 243 lol