The combat is absolutely not "press attack to win", and it's definitely not too easy once you turn Stronger Monsters on. In fact, even with Stronger Monsters off, you can keep the difficulty level where you want it by avoiding enemy encounters, which are never mandatory barring boss fights.

If you intend to get a Switch at one point, you should know that the Switch version has a demo that lasts 5-10 hours depending on your play style, so you won't have to buy it in order to find out whether you like it or not.

The Switch version is indeed better, but its graphics are worse, and the content you miss out on is more relevant to big DQ fans than to newcomers. There are dungeons based on past DQ games, which don't exist on the PS4 version. Aside from that, it's mostly just quality of life improvements, and small changes. Nothing major. I played the PS4 version for 110 hours and I don't regret it, it's still easily the best game on PS4 in my opinion, and I say that as someone who also got the platinum for Persona 5, Bloodborne, etc.