The title of this post, "Many 'saints' were wicked men," was one of the Reformers charges against the saint-venerating papists of the day. Off hand I cannot recall the Reformers providing many specific examples. Allow me to provide one: San Simon of Guatemala (reasonably full background).
San Simon is an example of a wicked man who lived a very colorful life. You can read more about it at the link above, if you like. His veneration started with friends, and caught on over time. Today, his veneration is not only clearly contrary to Reformed Christianity but even to conservative Catholicism (note that the blog I link to above is a Romanist blog, not a Reformed blog).
Is San Simon a "canonized" saint? No - I don't think so (I hope I'm not wrong about that). But he is venerated within a significant part of practical, real Catholicism. I don't mean that this practice matches the official doctrines of Catholicism, but actual baptized, communicant papists are buying San Simon's candles and making unChristian requests of this dead man.
What differentiates San Simon from other "saints" whose lives come down to us in legends? Perhaps the main differentiation is the preservation of his life history by virtue of the printing press. If there were less writing on the candle, or the prayer were a bit less ridiculously unorthodox, why would the memory of his wickedness be remembered? Is it hard to believe that legends sprang up about wicked men of the middle ages if it could happen in the modern age? Surely not.
I realize this doesn't fully vindicate the Reformers, but I hope it demonstrates that what the Reformers noted is not implausible, and is not just cranks complaints.