You’re right
First Lutheranism - still kept the True Presence of Christ in the Eucharist, priests, confessions too etc.
Then Calvinism junks the True Presence but kept the rest
Then Anglicans tried to merge the two.
Then in the 1600s you have Baptists who decide to junk out the baptism part (weird name) and the eucharist.
Then you have the wackadoodle millerites
Then you have Mormons, Jehovah’s witnesses, Seventh Day Adventists
Then you have Evangelicals including the Oneness Pentecostals who reject the Trinity - going the way of the Unitarians who are now “post-Christian”
Thing is that very few Protestants ever even tried to remain ‘unified’ in the way that RCs define the term.
Most Protestants will not condemn all others to eternal damnation like Roman Catholicism condemns all non-Catholic Christians too.
Actually you had the NT church, which, based upon the only wholly inspired substantive authoritative record of what the NT church believed which is Scripture, especially Acts thru Revelation (revealing (including how they understood the OT and gospels) did not manifestly believe in such distinctive RC teachings as,
The Lord's supper being a sacrifice for sins by (only) by the hands of a member of a separate class of sacerdotal believers (priests," and with conducting that being their main distinctive function, who dispensed the "true body and blood" of Christ as spiritual food, under the appearance of non-existent bread and wine. Thus presenting a christ whose appearance did not correspond to what he physically was (contrary to the evidence of that in Scripture which is emphasized in contrast to a false christ). See The Lord's_Supper.
Praying to created beings in Heaven, which is nowhere seen despite over 200 prayers by believers that are recorded by the Holy Spirit in Scripture.
Looking to Peter as the first of a line of infallible pope reigning from Rome. Which even research by Catholics provides evidence agains t.
Baptizing souls who could not repent and believe (or needed to) which itself saved them.
Preaching that souls must actually become good enough in character to be with God in Heaven, and since the sinful nature remained after baptism and manifested itself, then (except for a few rare subjects) they must needs ensure purgatorial sufferings in order to attain to this state, and atone for sins they failed to suffer enough for while in this world. View View
Manifestly affirming even proabortion, prosodomy public figures as members in life and in death, thus making them brethren with the rest.
Enough for now, but there is more since Rome exalts herself as uniquely being the one true church whom all are to submit to. We to varying degrees come too short of the NT church ourselves without adding to that by submission to a prostitute.
As a Trinitarian Pentecostal, I agree with you about the Oneness sect, but believing and standing on the Word alone, will NEVER seem wrong to me. In another state, I was a member of the Evangelical Covenant Church, whose creed is, “What does the Bible say?”. Personally, I can worship in any church which preaches Jesus Christ and Him crucified. I don’t have to agree with all other points, though I have strong beliefs on those other points. If I don’t agree with every single one of the teachings, big deal. I go to worship and pray. As long as the church believes in the Deity of Christ, his death, burial, resurrection, and ascension, the infallibility of the Word as originally written, and His coming return, I’m good. I could easily worship in a Catholic church, though I would not participate in their communion. Firstly because I know it would be against their rules, but also because I do not agree with their doctrine of transubstantiation, NOT because I would think I was sinning by partaking. I could NOT, however, worship in a Mormon or Jehovah Witness gathering, because they don’t believe in the Deity of Christ or the atonement.
Then you have those of us who consider ourselves of the Bereans persuasion.