Jody..
I would guestimate the PP in .22lr at 10-20% larger than the TPH, although I'm working from long memory on both. Obviously, I know the PP in either caliber is larger, as I believe I said that. As far as the TPH being thinner in the grip than a M21, heck, beats me. My memory isn't that good.
Now, is the PP a 'pocket' gun? Guess that is determined by the size of your pocket. There are very few true 'pocket' guns I would carry, as I don't like derringers, and most of the rest have I have caliber issues with, or the available offerings are of low quality. Anything in .22lr is better than nothing, when you need it. But I never cared for being under-gunned.
I have a M21. Don't really care for it, but it shoots, and it is pretty dang small, when that is important. The .22lr PP I had was ten times the gun, quality wise, and was certainly far more accurate. Put them on the table with any TPH, and I'll take the PP. Why? Because I like it. Nothing more. But if you put a PP, PPK or PPK/S in .380, I'll take any one of them first. Put down an AMT B/U in .380, I'll stick with the PP, 22 and all, and would take the TPH rather than the AMT. All this stuff is relative, and gets down to what one likes, shoots well, and is comfortable with.
By the way, I did some checking. The PP is an inch and a half longer than the TPH, and weighs 682 grams vs the TPH at 396. Like I said, a bit bigger, and yep, it's heavier, but not even two times so.