For the pros, in my opinion, it is better for the baseliners of the
tour to have two-handed backhands. Past history indicates that
baseliners with two-handers have had more of an all-court success.
Look at Agassi, Chang, Courier and Kricstein, for example. They
have done well on all surfaces. I don't see why Medvedev won't in
the future, either, and several others in the top 50.
Now look at the baseliners with one-handed backhands: Muster, Mancini,
Perez-Roldan, Jordi Arrese, etc. They are definitely thought of
as being more strictly clay courters (though Muster was just a point away
going to the US Open semifinals this year.) Lendl, of course,
is the big exception.
So, for the most part with some exceptions, baseliners with two-handed
backhands tend to do well on more than one surface.