What-if Magneto buttered up The Hulk/Bruce Banner?

[Animeality]

After being antagonized for years, Magneto appeals to both Bruce Banner and the Hulk by welcoming them into the Brotherhood of Mutants, accepting them as mutants and pointing out how General Ross and his "humans" have been hunting them. Magneto crafts an anti-Xavier helmet for Banner, and builds it with an expandable material that can fit The Hulk's head.

How screwed are the X-Men?

[TerryAce]

All the screwed unless they can get Doom to re-fuse Scarlet Witch with that magical entity again

[Stigmazilla]

All the screwed unless they can get Doom to re-fuse Scarlet Witch with that magical entity again

is that really so much worse then juggernaut?

[big_adventure]

It really isn't worse at all than Classic Juggy. Juggy is stronger, much more durable and has an "unstoppable" bonus power. The same ways to beat Juggy exist for HelmetHulk as well (ripping off the hat and TP'ing him, or BFR), plus HelmetHulk can simply be beaten with enough damage, something that doesn't really work with Juggy.

And it's still nothing on the level of a bunch of the X-Men's foes. Hell, the recruiter, in this situation, is Magneto, someone who would instantly slaughter most teams of X-Men at the bell, without his "don't wanna kill mutants" thing and/or PIS getting in the way.

[Anarchist]

Yup, to be precise, Hulk NEVER beat the Juggernaut once without using BFR, the Juggernaut being depowered or Hulk being amped (War Hulk).
Even during WWH (the X-Men really had it worst with being hit by PIS in favour for Hulk) Juggy was overpowering Bruce and had to be BFR'd.

And on the subject: There are people who could solo in SECONDS on several teams of the X-Men.
Take Magik for example, she will d-dump Bruce into Limbo at the bell.

[T-1000]

Actually, what would probably be the biggest problem for the X-men isn't so much the fact that they would have an enemy with this kind of power, it's the fact that someone with that kind of power is working for Magneto. Remember, Juggernaut usually works on his own, or with Tom Black, not Magneto. But if someone on that level started taking orders from the Brotherhood of Evil Mutants, I can totally see the X-men having a serious problem.