Ok, so keep in mind like 90% of the rest of this blog, the following is mostly just headcanon.
Retainers are AAHW units designed to keep people trapped in Hell, since Hell is more like a waiting room until someone can grab your 'soul' out of it and revive you somehow.
They are half mags so they're about twice the size of a normal grunt (meaning a good 10-15 feet tall)
Regeneration/healing factor
When Doc was in the AAHW, this was his job. Yes, he has fought Hank before. Hank has no idea.
In order to become one, Doc had to go through some really intense mental conditioning and reprogramming that the vast majority of agents would not be able to handle. The magnification process alone would have killed most grunts given the psychic powers it granted them.
Deimos, who worked as a MAG scientist (he was unable to be conditioned to be an agent), met Doc through the MAG program. While he wasn't the one in charge of actually turning Doc into a MAG, he helped Doc DE-Mag and reverse the conditioning process.
The process of getting the Retainer mask off tore Doc's face up, since the mask was fused to him. The skin on his cheeks is completely torn off, leaving his teeth completely exposed, though he still has lips. This is why he wears his current mask all the time.
The important thing to know here though is DOC STILL HAS HIS PSYCHIC ABILITIES and they are fucking strong. He could kill you with his mind if he really wanted to.
His abilities as a Retainer are what allows him to get Hank out of Hell so easily, and why he's more knowledgeable about the state of Nevada and how to stabilize it than anyone else. He knows about other universes and planes of existence because of his powers. They also allow him to easily heal people from things that really should not be healable. Like piecing together Sheriff's face after it was blown off with a shotgun, or just. Frankensteining Hank's body back together over and over.
All of that said though, Doc refuses to use his powers for fighting. If he ever uses his telekinesis against you, one, you're basically dead. Two, you really, really, fucked up and pushed him to his breaking point. Which is an achievement in itself because he has the patience of a saint.
Deep down, he fears losing control. He fears reverting back to his conditioning from the AAHW. He fears becoming an uncontrollable monster if he uses his powers. Therefore, he prefers to stay in the backline and not do any direct fighting himself. When he does fight, he uses long range weapons like snipers and rocket launchers.
tldr: Doc has really strong psychic powers but refuses to use them out of fear of losing control of himself.
Also fun fact. When Hank gets upset and in one of his moods, Doc will fistfight him to help Hank calm down and blow off steam. Sanford could do it, but Hank might genuinely try to kill him. Doc can handle and shrug off any murder attempts.
