I wouldn't blame the electrician here... I blame Stores like Home Depot for selling the Leviton Junk.
Years ago I installed a Leviton 6-50 and then when installing it, using only moderate torque, the white-metal threads of the attachment lug stripped. I threw the junk in the garbage and replaced it with Bryant.
I will only use Bryant or Hubbell for Continuous Loads such as EV car charging. As this Blog shows, installing Leviton is Borderline Criminal.
I'm really getting sick of Leviton in general. Home Depot as a for instance sells plenty of the Leviton Crap. Pull chain basement ceiling lights break after 4 on-off cycles, after REPEATED replacement - meaning nearly 100%
of them are Junk.
(The Legrande stuff at Lowe's is also made in China, but of a better quality).
What gets me is there is NOTHING in the new 2020 NEC addressing this. They have plenty of other really silly requirements - one of which is banning NEMA 14-60 plug-in circuits for the expected avalanche of 48 ampere fixed in place, or portable charging facilities (for all the new ev's coming out with 48 ampere chargers) - limiting such to either 30 or 50 ampere receptacles max. No matter that the 50 ampere receptacles from Leviton seem to melt down. Or that you can't have adjustable 'fixed in place' EVSE's any longer. Underwriter's Laboratories has been SUSPECT for years, as a for instance, this Leviton Total Crap gets a listing. They must have insisted on a Blind, Deaf and Dumb tester.
As far as the 6-50 or 14-50 debate, I think FORD has standardized on the 14-50 for their 'occasional use cord', so that means that the 14-50 receptacles will win, just like VHS supplanted the superior Betamax. Being best has nothing to do with most popular.
Many EV drivers to the boonies stop at camp grounds with 14-50, and TT-30 , ( but no 6-50 ) receptacles... I vote for 14-50 in the interest of standardization even though I hear the complaints of added cost..
But whatever you decide to install, avoid the 'firestarter' branded receptacles.