Hope it works well for you. I don't see how you are having a problem with .45 Colt recoil, if you let the gun roll in the hand like you're supposed to. Especially don't understand how its tough on your thumb, BUT, I don't have your hands/wrists, so...
.38s through that gun should be great. REAL .357s might not do so well in your hands. And tis not impossible for there to be a significant difference in point of impact between .38 and .357 in the gun. Shouldn't be, but I've seen it happen, so be aware it might.
Don't know where the Ruger bashers get their experience, mine have all been excellent. I've got 7 Ruger .45 SAs, my first bought new in 1983. None of them have ever had problems, all shoot well, none have ever had the cylinders touched or needed to. Not saying there aren't poor Rugers out there, but I've never seen one...
Seems like some folks buy a Ruger, because its not a Colt, then complain about it, because its not a Colt.
Enjoy your gun, keep the loads light. The birdshead grip is comfortable (though I don't care for the style) until you get around 200gr/1000fps (or equivalent) recoil, then, not so much, for most of us, anyway.
Enjoy!