maybe some "basic skill" yes. But trust me the diablo community is full of people unwilling to learn basic stuff, or just not trying (or dont wanna try).
At the end of the season I ran many 4 man grps (usually Im a solo player) with my wizard (so I was more or less the only paragon dependant class).
There was a huge difference between running 85, 90, 95 or 100+ just depending on what the barb/monk/wd did right or wrong.
Sometimes it was a struggle to do 90 and sometimes 99 was a 100% clear in time.
So yes, experience and proper play was a much more deciding factor than paragon was.
You could argue that it's only about the paragon when you always play with the same people who you know what they're doing. Then yes, paragon (and gear) of the DPS class is more or less the only thing you can try to improve to get higher in grifts (beside of RNG of course)