Ditto to Smilie - surprised at myself for forgetting to point that out, that she could well be bilaterally lame, but worse on one, so you're not recognising the better one. Of course, not at all saying that's the case, but always worth considering.
I'm also assuming it's the same foot the pony was lame on a month or few back? can't remember details, but didn't we think that was likely a stone bruise/abscess? Did we have hoof pics? If not, they would be helpful.
doesn't seem to be an abcess, as farrier found my little mule had an abscess when she first came to me, so I know what that looks like
Abscesses & bruising can manifest in many ways. Not infrequently I go to a client's horse & point out an abscess hole/crack that's been & gone & they say 'can't be - he wasn't even lame!' Sometimes there's nothing to see. Sometimes no obvious heat or inflammation. Sometimes a fat, hot leg & severely lame... Again, not saying it is that, but just because you can't see something obvious... If it is the same foot, been chronic 'offness' for that long, I would be thinking it's not just an abscess though.
Think after hearing others' thoughts and reading a lot more about those conditions, that maybe he was going too much on myths instead of real hard knowledge about those diseases.
...Or maybe has similar experience to me, in knowing how common it is & how bad it can get... that he's seeing fat horses & good grass & wanting you to take 'preventative action' so you don't have to go through that with them, along with a lot more hassle. Far better/easier to avoid than treat. I'd certainly advise to do your homework & take those concerns seriously too.