I think he's suffering from not being Mark Lenard. Mark's performance and demeanour is distinctive and unrivalled. It's a bit like how Benedict Cumberbatch is a fine actor but can't come close to being an equal of Montablban's for Khan. Frain just come across as just another Vulcan right now.I'm not sure I understand the complaints about Frain as Sarek. I don't have enough to go on yet to see how well he's doing. I really want him to succeed; perhaps I'm just dazzled by his outstanding performance on Orphan Black.
But it is called a nerve pinch so I assume its about the nervous system rather than the circulatory system. Looking at MA. Archer, Seven and Odo have done it. It also mentions that in Voyager it was said to resembles damage to the Trapezius nerve bundle.