I’ve had a number of Wintecs over the years (I keep selling them cheap to needy students) and they have been satisfactory for the OP’s purpose. I prefer the Pro, as I like a narrower twist, but the Isabell is a “nicer” saddle.
I agree with the idea of using a wider gullet and a fleece half-pad. I would encourage a bit of experimentation in this regard to get the best fit on an individual horse.
I currently have one wide, curved propane tank QH and a more TB-type guy; I am able to get adequate fits on both of them with Wintec or Bates saddles.
It does not sound like the OP is prepping for the Olympics in this case, so I would suggest that giving the Wintecs a try is not an unreasonable strategy.
Clearly, one poster here has had bad experiences; not the first, not the last. Others have had good experiences. Weigh the evidence and make a decision.
RE needing to re-tighten girths, etc. I would suggest that the synthetic materials soften somewhat from body warmth, both on the horse’s back and under the rider’s seat. The fit and comfort/depth of the saddle will change after the horse/rider/saddle warm up, and the warmup effect will not be completely retained by the saddle material. This is different from a well-broken-in custom-fit saddle. But then, they don’t cost $6K, either.