I agree the racial "blood" selections should have built-in negatives to keep them somewhat balanced in custom race creation.
Not seeing what is particularly over the top about the Ythril +20 weight and +1 attack, though. +1 attack is no big deal, and encumbrance isn't too much of an issue in the current build. Unless you mean it's just the matter of it being on *top* of the Juggernauts thing.
Frankly I think the Krax racial is far better, as an all-win ability with no downside (Fortify Tile + Blind will let relatively low level champions solo most dangerous, high value, high damage monsters by becoming effectively untouchable)
Maybe I'd be more impressed by the Juggernauts if the standard units that I built and my champions weren't already basically unstoppable to the AI, and the Juggernuats had more value. As it is, they sound fun, but unnecessary. Hopefully that will change with further polish.