It looks like a paddle holster would be great for quick on/off. Problem as I see it is that they are made to be worn with paddle between belt and pants with most of them having hooks to catch on belt.
Unfortunately my position choice of carry has a belt loop which means the paddle would need to be inside the waistband of pants. Is the extra thickness gonna be to do that gonna be a problem?
Not sure I would want the belt hooks on the paddle inside the pants.
Has anybody ever used a paddle holster with the paddle inside the pants, if so, how did it work for you?

Skip the paddle holster. If quick on/off is what you need, find a holster with snap belt loops.

It's more secure, more stable, and more concealable than a paddle, and also solves your pants belt loop issue.

Holsters like the Alessi CQC-S, Ritchie CQ-QR, RGrizzle Georgia Snap, TTGunleather Elite Snap, and similar.

I always carried (& loved) the Safariland paddle for off-duty concealment; paddle went inside the pant waist and the holster hooked onto the underside of the belt. I never needed to put the paddle between the belt & pant, and it worked exactly how you're looking for it to.

I carry my EDC in a Galco paddle and have for years. I put it inside my pants. Quick on quick off if I want and very secure.

Paddle holsters can be hit or miss. Make sure the make and model works for your belt/pants setup. The holster needs to stay in your pants 100% during the draw.

I fully agree with RogueJSK in that the double snap design works much better in my experience. I will add that I find that design more comfortable and even more form fitting to my ample waistline. HAHA
My $0.02 worth. YMMV