I considered the Mainship 350/390 a really great successor to their already-very-good '70s-'80s 34' models I, II, and III. Not perfect, I understand, but many of the things we thought might actually be improved on our Mainship III happened in the 350/390s. Many of those (e.g., side door at lower station) wouldn't have been possible without the wider beam...
The swim platform water intrusion thing is the only reported problem I'm aware of. (But we ended up going a different direction, so don't have first-hand experience.)
FWIW, we also shopped on the 43 and the 400, and they too had very nice features, including stairs to the flying bridge.
I would describe Mainships (and boats from their original/sister brand -- Silverton actually built the first Mainships) as very solid Chevies/Fords/Dodges, if that analogy makes sense to you.
Chesapeake Bay, USA