I do not know anything about the Waldensians. Specifically, do we actually know what their doctrine was and why the Catholic church opposed them?
Most information about the doctrine of first valdensians that survived till today is contained in the inquisition protocols. According to "New Advent":
are among their doctrines that contradicted roman catholic faith, so I think, that yes, they can be view as sui specie 'protoprotestants'.
Contemporary Waldenses were 'assimilated' into reformation.
Well. Some of what they said makes sense from a Protestant point of view, but not all. The biggest doctrinal "Holy cow I can't believe they said that," is
This would mean that if your local pastor was shacking up with someone, any baptism they performed would come into doubt. That goes against Augustine's teachings and all (I believe) of the thoughts of the first Reformers.
The Catholic Encyclopedia also implies that they borrowed from the Cathars, which would have put them clearly within the realm of "heretic."
In this book, one curious point is their outright rejection of asceticism. This, of course, goes directly against Christ's statement that certain demons could only be removed by "prayer and fasting" and Paul's allusion in 1 Cor. 9:27 (he speaks of "beating his body.")
There are some things listed here which are concerning (though it is hard to tell which is Cathar/Albigenses and what is Waldenses. Of course, they are interbred). Most importantly:
A bit of a side note: it seems that the first and foremost reason they were condemned was that they did not submit to the local authorities. They were instructed to visit with the bishop (who, at that time, was a lord) and they refused. When this obstinacy continued they were de facto criminals endorsing criminality (if you are summoned to court, you go to court. God does not give us free passes to get out of traffic tickets). Once they were condemned for this behavior by the local synod of bishops (a synod represents a small geographic area), their doctrines started to diverge from Catholic (and I would argue eventually even what could be passed as Christian) thought.