The newer Wintec 2000s have a nice deep (dropped) panel, great for adding extra wool in this area to support the correct arch width.
I've sent a message to one of the few local saddle fitters that I've found (Two Time Tack) to see what they have to say. The upside is that they do have Smith Worthington listed on their website, who do happen to make some suitable saddles that aren't $2000. I also like that SW offer saddles in a seat larger than 18" and some even with extra forward flaps (which I may or may not benefit from).
One thing I forgot, based on my last comment.
When you've gotten a horse from poor to good condition, as in Captain's case, or if you've lowned/looked after it for a long time, it sometimes won't tell you there's a problem with the saddle.
Heavier breeds are the worst for this sort of behaviour, and it's actually quite humbling when you meet one. It is for me, anyway. Because the horse has often put up with a great deal of discomfort rather than upset its owner/rider/carer by misbehaving.