I wouldn't go that far. Islam is a virulent heresy, no doubt, but most Protestant groupings aren't and nearly all Protestants are decent, good, Christians. Other groupins like the Moonies etc. are prety akin to Islam.
I have no disagreement with your statement other than the fact that both Islam and Protestantism are man-made churches. Like with Islam, their beginning is with a man. Protestants believe the Church was in apostasy for 1,500 years (Luther actually wanted only to reform some corrupt practices of individual clerics, and that grew into a whole new theology, new biblical canon, AND a man-made church)
Mainstream Protestants are Trinitarian Christians and, as such, our brothers. There is no comparison between them and ishamelite heretics as far as their beliefs are concerned.