I agree. The footnotes are much better in the NKJV. Do you think it is better to ignore that there is a major problem with this passage? Erasmus had doubts about the Comma Johanneum. You may think that this reading is correct, but no serious apologist will use this passage to defend the trinity precisely because it is in doubt. The NKJV footnote merely documents that there is a problem with this passage.

In John MacArthur’s Study Bible he notes:

5:7,8 in heaven: the Father, the Word, and the Holy Spirit… three that bear witness on earth. These words are a direct reference to the Trinity and what they say is accurate. External manuscript evidence, however, is against them being in the original epistle. They do not appear in any Greek Manuscripts dated before ca. tenth century A.D. Only 8 very late Gr. mss. contain the reading, and these contain the passage in what appears to be a translation from a late recension of the Latin Vulgate. Furthermore, 4 of those 8 mss. contain the passage as a variant reading written in the margin as a later addition to the manuscript. No Greek or Latin Father, even those involved in Trinitarian controversies, quote them; no ancient version except the Latin records them (not the Old Latin in its early form or the Vulgate). Internal evidence also militates against their presence, since they disrupt the sense of the writer’s thoughts. Most likely, the words were added much later to the text. There is no verse in Scripture which so explicitly states the obvious reality of the Trinity, although many passages imply it strongly. See 2 Cor. 13:14.