A top-2 runoff 2nd round definitely could be desirable with range voting.
It tends to compensate for strategy-caused distortions in the result from
plain range, because in the 2nd round A-vs-B runoff, all votes
(even by strategists) will be honest. And in computer simulations,
one indeed finds
that range+runoff is superior in terms of Bayesian Regret measurements,
to plain range, provided there are enough strategic voters in the voter-mix.
If, however, the voter-mix is mainly honest, then plain range is superior
to range+runoff.
Returning to the Condorcet issue, see
http://rangevoting.org/AppCW.html
http://rangevoting.org/CondAppConflict.html
which had made the point that with range or approval, PROVIDED the voters
employ a certain simple and fairly realistic strategy, a Condorcet winner
automatically will be elected.
That differs from using a Condorcet voting method as follows:
if a Condorcet winner (CW) [based on honest votes] exists, then:
VOTING METHOD.............Honest Voters............Strategic voters
Range............................can elect non-CW...............elects CW
Condorcet............................elects CW...............can elect non-CW
!!