jwfawcts much has been made of the fact George Howard presented his idea as a "theory". It's true he wasn't dogmatic, he didn't need to be. He wasn't a JW and his faith didn't depend on it. But did he believe he was correct about the divine name in the NT? Well obviously he did or else why make the argument and assemble all the evidence to make his case? Plus his later work continued the theme as he attempted to demonstrate that an early form of the book of Matthew in Hebrew used the divine name.
Additinally David Trobisch and Lloyd Gaston are more definite about the NT containing the divine name than George Howard was. Plus the work of Frank Shaw is suggestive as regards the divine name in early Christianity.
There is a lot of evidence for the divine name in the NT, including scribal practice in the period, statements about the divine name in the NT, continued Jewish use of IAW and other forms, the nomina sacra in early Christian manuscripts, the high number of variants involving Kyrios, Jewish statements about the divine name in gospels, removal of the divine name from the later LXX and so on.
You should acknowledge that there is a lot of evidence for the divine name in the NT, even if you personally don't find the evidence compelling. The unthinking mantra "there is no evidence" is false and empty evangelical apologetic rhetoric.