That's one, of many, things I didn't like about Wolverine: How the adamantium thing was played. It had always seemed to be and had been inferred that Wolverine went through something like a vivisection to graft the adamantium to his skeleton, one bone, piece, or whatever at a time. Through a complicated and painful process.
Pumping him full of the shit hardly seems to me like as being "as bad" and it sort of begs the question how the stuff perfectly formed around his skeleton and even managed to form nicely formed, sharpened, blades around his claws.
The adamantium thing was "played" exactly how it was shown in X2 when Wolverine fought Deathstrike in the adamantium bonding lab. The adamantium had to remain molten to be molded to the bone, it was shot through injectors directly into the body, and then it cooled internally. Remember how Wolverine finally defeated her by injecting her with adamantium until it was coming out of her eyes?
Wolverine was remarkably consistent with
X2 in that regard.
It seems to me that being injected full of molten metal would fall under the "pretty bad" end of the pain scale any way you cut it, vivisection or no.
If you have a problem with it, it's not a problem unique to
XMO: Wolverine by any means. It's a problem with the very premise of post-adamantium Wolverine in its entirety, either in the comics or in the movies. And once it gets to that scale, you might as well just forget it since you're dealing with mutants who can move cities with their minds and freeze oceans.