This has weaknesses vs inverted and I don't think the strengths make up for it. There is a reason he is the only one.
Agree that the SP's have some weaknesses compared to inverted...but all rubbers are a trade off and do some things better and some things worse than other rubber types. That's why I say a fast and spinny SP like the one Mattias uses; something that is relatively close to an inverted as far as SP's go, rather than just any old SP.
Most top players don't use this set up, I agree...but then most top players have been developing their skills over many years and wont have necessarily done that with the rubbers that are the most viable for the game
as it exists at this particular point in time. I just think Mattias Falck got lucky in the sense that he's been using a particular set-up for many years, and it just so happens (in my opinion) to be a set up that's particularly well suited
to the game in its present state. Notice how Mattias has shot up the rankings in a time period that coincides with the introduction of the plastic ball - that could well be the evidence I'm looking for to back up my theory, although I can't say definitively that it is, of course, because there are too many other unaccountable variables!
I just think that a fast and spinny SP on FH and an inverted on backhand is the most viable arrangement for a modern, close-to-the-table power game in the plastic ball era, whilst the inverted on the BH allows a lot of aggressive BH play, particularly over the table flicks etc.
Would Harimoto be a better player today than he currently is if he'd have always used a fast and Spinny SP on FH from day 1 of his training? We'll never know, of course...but it's an interesting thought!