Goliath Monk question

As I read it, the Goliath Monk can use its large form to make themselves a large creature capable of grappling a huge creature (dragon?)

now if an enlarged spell is cast upon this large form, it should make then make the monk huge? Large form does not, itself, appear to be a spell or spell effect. I think of it more like a barbarian going into rage, that category.

I realize RAW, the hill giant can only tumble up to large, but as a DM, assuming the shenanigans to make the monk huge work, would you allow the now huge monk to tumble another huge creature?

I have visions of Antman going huge and punching the large flying carrier type Chitauri, knocking it down to the ground.

I also have visions of a huge monk grappling the gargantuan tarrasque (one size difference, right?) and dragging it around. Ultraman v. Godzilla!