That's not true at all. Musical and liturgical issues set more denominations apart than theological or scriptural issues.
Which music do the large number of Protestant Churches now ordaining women and queers as well as marrying one queer to another, approving of abortion, etc., prefer? Show Tunes, Disco, House Music?
It's nowhere near that simple and not nearly that easy to dismiss the differences. You could probably narrow that tens of thousands down to just thousands, but not to the point that it's an insignificant number of different doctrines and doctrinal disputes. Thousands rather than tens of thousands isn't much of an improvement and still proves that those among the thousands do not constitute the One True Church. Even if you try to play games by pretending the "Invisible" and "essential and nonessential" doctrines paper over the differences there's no way to deny that thousands of different churches couldn't happen were the Holy Spirit leading all those churches or even the majority of them. The fact is, all three legs of the Protestant stool have been sinking into the mud of self-interpretation ever since Luther iced the cake Wycliffe baked by shedding the sacraments and all authority other than Luther.
Like it or not, most non-Catholics in this country today belong to The Invisible Church of The Most High Self the same as so many Catholics have ceased to be Catholic and instead become members of that same church. Such folks worship the Most High Self no matter what they claim to the contrary. Satan is a past master of divide and conquer tactics and he's hands down defeating those who claim which church they attend doesn't matter, that they're their own church, that they can worship alone, that they only need the Bible and not fellowship, and so forth. All of those are just different ways to make yourself an easy lunch for the Deceiver who as a roaring lion, goeth about seeking whom he may devour.
The One, Holy, Catholic, and Apostolic Church is the Church Christ Himself founded and entrusted to the care of his Apostles. If you don't like that or don't believe that, fine, but don't claim that Christ would abandon His flock for fifteen hundred plus years or allow a lie with His name on it spread throughout the world while the few "real" Christians huddled in caves hording their virgin lamp oil, or that the heretics throughout history were the "real" Christians. Not only does such hokum slander both Christ and the Holy Spirit by calling both of the liars who cannot keep their promises, it marks you as both gullible and too lazy to study Christianity rather than just soaking up cliches. Just admit that you don't think Christ cares if you're a member of His Church, or that Christ doesn't care that His Father said He wanted none to perish.
There's no sense in playing Russian Roulette but telling others you're really just checking to see if the gun is loaded, fess up to playing Russian Roulette and go on about your business without slandering Christ and the Holy Ghost.