The problem he has is he's already admitted he can't control himself sexually, has shown a lack of respect for "girls" (they are simply something for him to use for his own gratification), and the same excuse he uses for his lack of control shows up in those chat messages.
It's not a leap to think that this excuse is something he's found valuable, because he's used it before both to get away with things and to get what he wants.
We already know he was in trouble for sex chats, again, from his own admission in his own book which I believe he said in his video was to pre-empt someone trying to expose it (but does he truly reveal all the details?), and that his wife found out about it. He himself repeatedly refers to them as "girls", so he can't complain if people interpret it exactly as written (and its repeated in his video). It's certainly possible that part of his wife finding out and reporting it was passing on the evidence, and / or also getting advice from someone, a close relative for example, which would explain how a copy came to be.
I don't know whether those messages are legit or not, but I do know they appear to be from the time stated on them for technical reasons, they match his MO in terms of the excuse he likes to trot out and they align with the pieces of a story we've already been told (and I think, prior to him telling it, so they weren't based on that). They don't stand out as odd or a contradiction to anything, in fact they fill in and explain some things.
For instance, we even have the "weird" situation where Mr Activist claims to have something on the WTS, but won't release it, and wouldn't record his own judicial committee, which makes it appear that what he has on them is something todo with himself. The 3rd party info about what happened in the congregations with elders stepping down and his father using his authority also makes this credible. Especially when you add the subsequent moving to Croatia, which he describes using the expression "we had to leave the UK" which again, is something the accusation of the messages explains, more pieces of a jigsaw fitting together perfectly.
To me, it all seems credible, it matches what we know of him, the overall narrative of the story, and explains some of the missing pieces that would still need some other explanation.
That doesn't mean it's true of course.
If it isn't true, then there are major plot-gaps that would still need some other explanation.
But as slimboyfat says, I doubt we'll ever get a truly satisfactory outcome unless he does a major come-to-jesus confession or a witness comes forward. His denials still leave gaps and as much as he thinks people treat him as public enemy number one, to many of us he's just an obnoxious jerk that we don't want anything more todo with ... I can't honestly see anyone going to such lengths to try to frame someone, or somehow know that they would subsequently act in a way that would make such stories (from way earlier) look so believable. So "smear campaign by haters" is simply far too convenient.