Unlike the Alexandrian mss, the Antioch manuscripts have vast agreement. This is undisputable.
If someone gave you a book that was nearly 100% as accurate as the original, do you think you could tell what the author wrote? Of course you could. The fact that so many manuscripts (over 5000) were copied so accurately and over such a widespread area, and over such a long period of time is in itself a miracle. What makes all this even more remarkable is that these were copied not by professional scribes, as was the case with the Jews, but by many gentile believers.
You mentioned 1 John 5: 7 as an example of your position. I don't know about you, but when I went out in field service and someone quoted that scripture I repeated the WT line that that scripture reading wasn't found in any greek manuscripts earlier than the 14 century (in my memory serves me correct). The NWT footnote states catagorically that it was simply "added in later Greek Manuscripts."
Now to my WT educated mind, this seemed like an open and shut case of some heretical trinitarian monk practicing his evil. Later research revealed the following:
1) 200 - Tertullian quotes the verse (Gill, "An exposition of the NT", Vol 2, pp. 907-8)
A) Vigilius Tapensis (MPL, vol. 62, col. 243)
B) Victor Vitensis (Vienna, vol. vii, p. 60)
C) Fulgentius (MPL, vol. 65, col. 500)
2) 250 - Cyprian, who writes, "And again concerning the Father and the Son and the Holy Spirit it is written: 'and the Three are One'" (Vienna, vol. iii, p. 215)
3) 350 - Priscillian cites the verse (Vienna, vol. xviii, p. 6)
4) 350 - Idacius Clarus cites the verse (MPL, vol. 62, col. 359)
5) 350 - Athanasius cites the verse (Gill)
6) 415 - Council of Carthage appeals to the verse as a basic text proving a fundamental doctrine when contending with the Arians (Ruckman, "History of the NT Church", Vol. I, p. 146)
7) 450-530 - several orthodox African writers quote the verse when defending the doctrine of [Christ] ... against the gainsaying of the Vandals. These writers are:
8) 500 - Cassiodorus cites the verse (MPL, vol. 70, col. 1373)
9) 550 - Old Latin ms r has the verse
10) 550 - The "Speculum" contains the verse
11) 750 - Wianburgensis cites the verse
12) 800 - Jerome's Vulgate includes the verse
13) 1150 - minuscule ms 88 in the margin
14) 1200-1400 - Waldensian Bibles have the verse
15) 1500 - ms 61 has the verse
16) various witnesses cited in Nestle's 26th edition for a replacement of the text as it stands with the Comma: 221 v.l.;2318 vg[cl]; 629; 61; 88; 429 v.l.; 636 v.l.; 918; l; r; and other important Latin mss.
So, if early Church fathers quoted this verse, then obviously it was used back then and wasn't invented by a Trinitarian monk like the WT claims. It is analysis like these that the few kinks in the mss underlying the TR can be worked out...if a person wants to work them out.
By contrast, the Alexandrian Texts have over 3000 places they differ from the TR and omit a volume of text which is the equivalent of 1st and 2nd Peter.
I am not a KJ Onlyist. I accept by faith that the Textus Receptus, which the KJV is based on, is the representation of the originals that God has by his providence provided. I believe that the originals were inspired but that the TR has everything needed to determine sound doctrine.