The Difference between McCoy and Archer is that McCoy had a personality, and OH what a personality he had! So while McCoy resisted the integration process, Archer was mellow enough not to notice his identity being drowned like an unwanted kitten.
Archer didn't go insane. He became calm and focussed and smarter. He talked about how centred he was and how he had information at his finger tips which he shouldn't have had.
We talk about Spock being Half Vulcan but do we really expect less of him for suppressing his Vulcan emotions + Human emotions? Who had the more volitile katra? The hybrid test driving the process or the first guy to perfect the process who was born no different from a Romulan who'd been a disembodied soul transferring between many consciousnesses for the last two thousand years?
Guzzling down Spock or Surek, would be like comparing orange Jiuce to antifreeze which would both surely be having completely different effects on a persons constitution as they're trying to hold this stuff down?
Please note.
Spock gave McCoy his katra, and then he stood up and saved Enterprise by fiddling with the engine AND THEN had that infamous little talk with Kirk "I am and always have been your friend." all the long while HE HAD NO SOUL! No Katra... Surely if those 16 grams that go missing upon death is a soul and no one can live without a soul... Exactly what sort of Xombie was Spock in his final scene during The Wrath of Khan was he supposed to be that Spock was at his most human when he was already dispossessed of his spark and divine essence?
Or he just sent McCoy a "Copy" of his personality.
Since Spock is half human, does he have a soul, a katra or So-tra? And since he has half a human soul, does that make him half real? Does that also mean that when he "headmailed" his "marbles" to McCoy that none of his human soul of what ever percentage he was allowed by god to have that he did not transfer over that information into the crotchety Doctor?
So Spock just headmailed a zip file of his electroencephalograms or some such pseudomedical gobblygook onto a new server. His actual Katra/soul went to Vulcan heaven like it was supposed to and... I was Thinking of Ralph Oppenhiemer C.E.O, the soccer mom and the honkytonk man... From TNG The Neutral Zone, they all died. Their souls went to heaven. Okay, Ralph's went to hell, but when Beverly revived them, did their souls come back from heaven or did they grow new souls or do they walk and talk and live "Lives" soullessly? ...Or did their souls wait in those frozen bodies for 400 years on the off chance their might be a little more "life" in store for them?