What separates the witlesses from other religions is the degree to which they cut members off from society. True, the Catholic church is the most successful cult of all time (hey, they even started the First Dark Ages!). However, now that they have competition, they have been forced to integrate into society at large. Hence, Catholics are not required to shun people that are not Catholics (including those who left the Catholic church). Catholics are allowed to celebrate holidays and birthdays, and do just about anything that defines normal society.
No, I am not saying that they have the truth. In fact, they edited the Bible to suit their needs when they first got started. They do practice mysticism, and they do try to guilt people into believing the rules that Paul himself misinterpreted. (Notably, the Protestants have inherited the Catholic Bible and also practice mysticism, though to a slightly lesser degree).
What makes the witlesses so much worse is the degree that they create problems for members where none needed exist. Notice all the rules for courtship (which do not exist in the Catholic church). Notice all the rules about music (as a Catholic, I could listen to pretty much any mainstream music I wanted). They have rules against after-school activities (as a Catholic, I was allowed to join Cub Scouts, sports, and whatever I wanted that was officially sanctioned by the school). There are rules against playing with worldly classmates (Catholics have no such rules). The witlesses have rules against college that Catholics do not. As a Catholic, I was allowed a reasonable amount of play time (no field circus), all the holidays including birthdays, and any toys that we could afford.
How does that compare with the witlesses? No courtship. They are in the process of banning most toys (Barbie dolls seem to be on the chopping block). No music except Kingdumb Maladies (unless you want Brother Hounder, who does not work for the Catholic church, to get you). No holidays. Play time usurped for field circus. I definitely think that is a significant difference.