Chekov should never have sat in the captain's chair in my view. He struck me as an intellectual with pretty limited command ability, particularly when you compare him to Uhura whose air of authority was ten times what he had! It was largely due to his being used as comic relief due to that wacky accent.
I always thought it was odd that he was meant to be security chief in TMP too. He was short, often beaten up in TOS, and wasn't a great shot with a phaser. Weapons officer makes sense but security chief? And as vindication of my opinion, just watch his shambolic investigation in STVI where he has to be led by the nose by Valeris who has no real interest in seeking him locate the culprits!
First officer on a science vessel was where Chekov's career should have halted in my view!
...and let's not forget, he didn't even seem to know in ST VI that if you fire a phaser on vaporize, and alarm goes off (in the galley Re: the gravity boots, he says, "Vhy not just waporize them?") - Academy graduate Valaris had to show him! Some security chief! NuChekov in ST XI seems to have inherited more brains!

(I think someone once suggested on this forum that Chekov in ST XI must have had at least one different parent, since he seems quite different than original Chekov, who was definitely no "boy genius" - maybe one of his parents in the prime universe was a crewmember on the Kelvin when Nero attacked, and was killed - the other parent remarried and named their child "Pavel" anyways?
Who would win in a fight between security chiefs - original Chekov or Worf? Keep in mind how Ensign Chekov did against the Klingons in the bar fight in "Trouble with Tribbles" - those punches didn't do much!)