Saying the Immaculate Conception was "created" in 1854 and the Assumption was "created" in 1950 is a lot like saying that gravity was "created" when Newton defined it.
But putting aside these two beliefs, let me ask you this, why do you and others have such a difficult time with perpetual virginity? Nowhere is scripture does it state that Mary had other children. The Lord entrusted Mary to John at the Crucifixion, this would seem unnecessary if He had siblings. Neither James nor Jude identify themselves as our Lord's broher. Perpetual virginity in no way impeeds Protestant teachings about man's sinful nature. Lutheran teaching has never questioned this. Luther, Calvin and Wesley defended it. Wesley didn't leave the Catholic Church, so there's no way to say that this was an idea he just "held onto."
But putting aside these two beliefs, let me ask you this, why do you and others have such a difficult time with perpetual virginity? Nowhere is scripture does it state that Mary had other children. There are numerous places that indicate she was not a perpetual virgin. Catholics (and a few early Protestants like Luther and Calvin) give weak arguments. There is this verse:
Mat 1:25 but kept her a virgin until she gave birth to a Son; and he called His name Jesus.
Even just an honest careful reading of this verse strongly suggest Joseph had relationship after the birth of Christ. A few people normally response to this verse saying, "Yes but "until" doesn't mean that Joseph had relationships afterwards." (Calvin does this.) I don't think that is being honest with what the scripture is saying. I don't know why Matthew bothered phrasing it this way to begin with if that isn't what he meant.
Then, of course there is all the times Jesus' brothers are mentioned, such as:
Mat 12:46-50 While He was still speaking to the crowds, behold, His mother and brothers were standing outside, seeking to speak to Him. Someone said to Him, "Behold, Your mother and Your brothers are standing outside seeking to speak to You." But Jesus answered the one who was telling Him and said, "Who is My mother and who are My brothers?" And stretching out His hand toward His disciples, He said, "Behold My mother and My brothers! For whoever does the will of My Father who is in heaven, he is My brother and sister and mother."
People usually respond to these (numerous) verses as, our Lord was talking about His mother and His cousins; as if a whole slew of relatives descended on Him for a family reunion. That's what He gets for turning the water into wine. Of course this overlooks the fact that the term "cousin" (Luke 1:36) is used in scripture and it is not the same word. BTW-Does this sound like a Lord Jesus who is bent on every word that His mother says? They wanted just to speak to Him but He certainly didn't run to the door.
Then there is the time Paul referred to "the Lord's brothers" (1 Corth 9:5). Or when both Paul and Jude mentions James to be "the Lord's brother" (Gal 1:19 and Jude 1:1) but this also is some relative.
These are a few of about 10-20 various examples that Mary was not a perpetual virgin. Most are explained away as the meaning is really cousin or, as in Matthew's case, it doesn't mean what it says. It's somewhat similar to b-d example of the sacrifice that was presented by Mary and Joseph about opening up the womb. Some people just ignore it.