Back when I used to have a G17, I used to shoot low all the time, so much so that I would compensate by raising the front sight up above the rear sight in my sight picture (not an ideal solution, accuracy suffered pretty badly). I should have tried some higher rear sights, but instead I just sold the gun and moved on to other guns.
Then, a few years later I started shooting friends G19's with Bar-Sto and Storm Lake barrels, and they shot really, really well for me. Much more accurate and right to point of aim with a normal sight picture. Back when I had my G17 I thought it was the lock-up, the tolerances, etc., etc. Now I have no idea what it was.
I bought my own G19 with a black Lone Wolf barrel recently and it is just awesome. Shoots right to point of aim with a standard sight picture. The sights are the stock plastic ones. Rear sight is the normal 6.5mm (one line). I'm thinking of going with the night sights, but it shoots really well without them.
I don't know if it is grip or what. All I can say is that shooting does vary model to model with GLOCK to some degree, even between calibre.
(And yes, I have tried other people's 17 off and on over the years. They still shoot below average for me. They are obviously a good design. The small differences do seem to produce different results in different shooters though).