My contention is that they almost certainly would have sold for higher prices.
I should also take this opportunity to correct myself and acknowledge that the one other thing that will negate the impact of significant M-R taxes is time itself. In twenty years or so, they should be paid off and become a non-factor (and this may well occur more quickly than inflation will numb the hit).
I’ve heard anecdotally that the M-R assessments can be extended, but I have no idea how often it occurs to any meaningful extent.
A buyer today would still be wise to not overrate such long-term effects, however. That is, be careful not to put too much stock into the 30-year (or 20-) argument as many homeowners never get there. If instead, it’s honestly your home to die in, then yes, your kids might not be so affected by your currently (outrageous) Mello-Roos.