Did you not look at the dimensions listed above? The Pixel 3 is narrower. What gets me is the weight difference. 2+ ounces.
I compared my pixel 3XL in person with both the pixel 6 and 6 Pro.... both the 6's are narrower than my XL, because they have a narrower, taller aspect ratio. And because they have much less top and bottom bezels than my XL, the 6 is shorter, and the Pro is pretty much the same height. If you've owned a 3XL, or something with a similar aspect ratio and size to that, the pixel 6's are going to feel smaller in the hand and fit better in the pocket
After hearing how big they were supposed to be, especially the Pro, I went in expecting to see monsters lol. That wasn't the case. Imo their size is overblown. But I am a tall guy with big hands, so that might make a slight difference
It does go to show you should always try and see a phone in person, everyone's idea of size and portability is going to be different.
Also the weight difference wasn't that noticable to me holding them.... but the Z Fold 3 on the other hand felt like quite the chunk
lol