Loki should have a legendary logia fruit or paramecia fruit
Tired of legendary fruits being myhtical zoan fruits
Knowing Oda tho, tongue out and a forest full of wolfs, might already be the clues we need in a sense.
Add that most of the nation might not be sufficient haki users, thus him being a logia user might not make sense.
Imo it's likely that he really has an extremely powerful mythical Zoan DF and they needed tons of giants to physically pin him down or some.
Atleast that's how I can make sense out of it.
Anyway any S-class DF will hit haaard on a giant. Normal DF moves are like 10times bigger and such, it should be ridiculous either way.
Edit: Or atleast I'd lean towards a Zoan or a Paramecia.