Very few Protestant traditions, if any, reject beliefs or practices simply because they are held or observed by another tradition. It might seem that way sometimes, but they almost always have some other reason (usually, that they find it to be contrary to Scripture).
Protestantism isn't a monolithic movement – within it, the founders of some traditions rejected relatively few Catholic teachings, due to their belief that Catholicism only fell away from the truth slowly (see, for example, Luther's perspective). Others rejected much more, and sought to re-establish the "primitive" or "apostolic" church based on biblical evidence alone.
So, for example, the reformers didn't get rid of the doctrine of the Trinity (also defined at Nicea). Most didn't get rid of infant baptism, though their understanding of it changed. They didn't get rid of Sunday worship, even though the biblical evidence for Sunday meetings is scant. And, similarly, they didn't find anything wrong with the Western church's dating for Easter, so they kept it.
As an aside, some Protestant traditions do take issue with the observance of Easter (regardless of its date), but for this position they have biblical and theological arguments much more sophisticated than "we don't want to be like the Catholics."
If you think about it, if being "anti-Catholic" were the defining characteristic, Protestants wouldn't believe in God, or the Bible, or salvation, simply "because Catholics do." Theoretically they wouldn't eat food or drink water or breathe air either, for fear of being like those Catholics! So hopefully it's now obvious that there's much more to Protestant vs. Catholic differences than that.