100%IV T-Rex and Moltres from "Preminm Raid Pass"
Hi folks, I never spend money on this game. However, I save $ from Gym each day. During this week, I spend my first $ on special box cost 480$. Got 6 Passes, many days ago, I spend my first Premium Raid Pass on Moltres and I had it ran away with CP1870. Today, I spend another Premium Raid Pass, and I meet 100% T-Rex. That's not miracle, those passes from Special box will bring you high IVs.
P.S., It's only the fifth T-Rex raids in my career.

Answers
Got a 100% Tyranitar on the first week raids went out, using my free raid pass. Got my first high IV lugia (96%) today from a free raid pass too.
Previously I had a total of 27 Lugia raids done, 9/27 catched, none of them above 82%(either seen or caught because I checked the numbers for high iv raid bosses), and like 90% of them done with premium passes. So no, it is just luck.
Hmmm, kinda doubt theres any sort of correlation here, just from two good outcomes.
Dont be so certain just because you had good luck twice within a short period of time.
I bet you have had plenty of similar 'luck' in various elements of the game, and through the free parts too...but they dont get counted or seem relevant.
For example....im sure you have had good hatches from the free incubator, but that doesnt mean 'free to play > payed incubators' and not buying incubators rewards you better IVs !!
And im sure at some point, a free daily pass has earned you atleast something good from a raid capture.
Its just rng...luck...chance. simple as that. Sorry dude.
(Also if Niantic did give better chances for payed passes it would destroy their reputation...all for something so unnoticeable, they just wouldnt do it)