See now that was my problem with Vic: he was Kirk on helium. Also ten years too old, but for the most part his performance was good. He just lacked the one thing that Shatner had buckets of: charisma.For the most part Vic Mignogna was fine was Kirk.
Haberkorn was also mostly fine as Spock. What got to me most was the pitch of Haberkorn's voice which was higher than Nimoy's, but not a big deal.
As I said upthread although Chuck Huber looked sorta/remotely more like Deforest Kelley I actually preferred Larry Nemecek's performance. He seemed more at ease and less forced. And he didn't come across as grouchy--a cliche too many seem to buy into about McCoy.
I preferred Huber, but honestly the only one of the fan actors to get it close was John Kelley in NV. Right down to the wig. He leaned less on the "Dammit Jim" than the others did. People do forget that McCoy was often light and good humored. Just don't get him riled up. He was supposed to be kinda like Doc Adams on Gunsmoke, but not a carbon copy.
The problem with Scotty is nobody on these things knows how to write him. I get that the character was mostly on Trek to spout technical jargon and be excitable sometimes, but the fan films lean way to hard into the panic and "Scottyisms." It started with New Voyages with lines like "It's time to ring the dinner bell! All right beastie! Come and get it." Oh my God, Scotty, shut uppppp!Chris Doohan was fine as Scotty. Indeed he even seemed to dial back some of the excitability that James Doohan exhibited in TOS's third season, which I appreciated.
It spilled over to STC with an ample supply of "beasties" and other homilies. Chris Doohan rarely alters his delivery and sometimes chews on the overbaked lines. Not every line has to be spit out. He should have watched more of his own dad's work.
Wyatt Lenhart as Chekov was mostly okay, but he could come across as a bit awkward as if he was playing Chekov as trying too hard to make an impression.
I feel like he had trouble with the accent which hampered his performance. And, again, it helps to write dialog that compliments rather than hinders the required accent.
Like you, I had no issues with the performances of the newer characters. I actually like M'Benga more in STC than SNW.