Funny thing about the Glock 21. I have smaller hands too. Actually average size palms and thumbs with slightly short fingers. The Glock 21 felt big to me, but I shot it really well. This was a first gen. model back in 1997. They're more comfy now, with the finger grooves.
I never shot a Glock 21 SF, but I have shot a 30. (compact 45) For me, it was no more accurate than the 21, and the magazine pinched my pinky finger. FAIL.
I owned a Glock 34 (competition 9mm) and shot it well enough to be combat accurate, but I could not get good groups with it at 25 yards due to the trigger. Remember, they were designed as combat guns, not target guns.
For my first centerfire handgun, (again, back in '97) I went with the Ruger P90 in favor of the Glock 21. I really wanted that Glock, but it was $100 more expensive, and the SA trigger on the Ruger was much easier to shoot than the Safe Action trigger of the Glock. I have no regrets.
Just a month or two ago, I bought my first (and probably last) 1911. There is such a wide range of them. A basic combat-level model does not (in my experience) shoot any better than any other combat 45, except for the first round. The single action trigger is actually pretty heavy. The best groups I've ever shot with a 45 ACP handgun were with my S&W 625, 5", HK USP Expert, and an EAA competition gun. Still the 1911 can be tuned up. For the rest of them, they are what they are. It's just that I'd rather have something that shoots really wall out of the box, than something that shoots OK out of the box, and will continue to shoot better as I throw more money at it. My basic 1911 (Para GI Expert) cost $550. My used S&W 625 cost $600. HKs new, go for around $900, ditto for the EAA competition gun.
Oh, speaking of tuning up, my Glock 34 had the lighter trigger than stock. Lightness isn't everything. It was still spongy. And the extended mag release was always digging into my thumb.
I'm forgetting the Beretta PX4 in 45. That was a great shooter too. That one had a laser though, so it was exceedingly easy to shoot well at the range. Those guns feel great and have good DA/SA triggers. You just have to like the looks, which are unconventional.
So there you have my experience on the matter, for whatever it's worth.