I'd say that
@Palmolive fox has pretty well summed it up.
However, if you are specifically looking for modern stainless adjustables, other than the Rex, the choice is pretty limited. There was a Barbaros/Rocnel adjustable, but I think it was sold only (or mainly) in the USA, and doesn't appear to be in production. There is also the recently-announced Tatara Muramasa, which is at pre-order stage and is very expensive. The Tatara website gives a lot of detail on it, and there is discussion here and there about it. No doubt others can come up with some more.
As well as the Parker and other adjustables mentioned above, the Merkur Progress, and its customised variants Digress and Mergress, is a decent zamak razor, which I find "mild", and the two best-known vintage Gillette adjustables, the "Slim" and the "Fat Boy", are on the "mild" side at the lower end of the dial.
I have a Rockwell 6S, in the original Kickstarter version with the replacement plates, and I presume the current version is identical. I'm always looking for a smooth, comfortable shave in one, and no more than two passes, and find that plate No. 4 gives me the best results.
Getting the desired results is, as
@Palmolive fox says, a matter of technique and practice. Whilst some razors are more docile in use than others, I'd suggest that not many of the better-known ones cannot, in time, be mastered; provided that you stay away from the really brutal (to me, that is) oddities like the Ikon Tech. It's probably worthwhile persevering with the Rockwell for the time being. If you do decide you want to go for an adjustable, the non-stainless versions are a good starting point, at a sensible price.