But, basically, yeah. Not every psyker is a violently raving wreck.
I'm less thinking "violently raving wreck" and more "evidently a psyker to everyone around them." Even if only in the fact that they are reverse-Pariahs.
(Well, let me phrase it this way: Amets got taken completely from the planet,
Nope. Training was done on-world (or in orbit/another world in the system, maybe; wherever the local Imperial presence is concentrated). This isn't a petty distinction; the galaxy is a really fucking big place, and Warp travel, while much much FTL, is still very far from instantaneous; the trip on the Black Ship is likely to have taken years each way, especially considering that Barrablanca is probably not in the Segmentum Solar.
moved onto a world of strange marvels and technologies
Metaphorically, yes, but literally only the last bit.
and went through the required assessing, training
Yep.
and sanctioning,
Nope.
had parts of him replaced with metal- and managed this from a tech-fearing planet
Yep.
with (relatively speaking) no mental or social ill effects? Okay then.
Hahahahahahahahahahahahahahahahahahahahahahahaha etc.
It's not the best comparison, but not every character from one of the odder sections of the Imperium is as totally deranged as the average depiction.)
It's less "not as totally deranged as the average depiction" and more "won three lotteries within a year of one another." Not technically impossible, mind, but, well.
Edit: Actually, make that four lotteries: Getting a desired result from Imperial Bureaucracy within a short period of time? Mother of God(Emperor of Man).