Pretty much the opposite of "git gud", honestly. EDH is the format where the answer is usually telling people to get less good. If someone's blatantly playing at a far more competitive level than the rest of the group, the passive-aggressive solution is usually to hard focus them as a table until they start presenting less of a threat, while the mature solution is to talk to them about it and ask them if they can't play a deck more in line with the group's meta.
I don't think even CDH players would tell you to "git gud" unless you're specifically trying to play at CDH tables. That's not really what the format's about.
As far as shuffling due to fetches and tutors goes, encourage sub-competitive "signalling"; basically the opposite of what you're trained to do in competitive Magic (ie, search at the last second). When someone plays a fetch they should be cracking it immediately, telling the table what they're searching for, and either playing a card as if they already found the land and have the mana or passing while they shuffle up. When someone plays a tutor, if it's a show-and-tell tutor they should just tell the table what they're searching for and let play continue; if it's a secret tutor, they should be honest and if they aren't going to play the card immediately just tell the table to continue while they search and shuffle.
The player in question might not even be intending to/wanting to hold priority while they're searching, and just following the "proper" procedures because in lieu of permission to do otherwise it's the obvious thing to do. You might want to check with them in a non-confrontational fashion first.