Dessert Nomad
Adventurer
Personally, I can suspend some_level_of disbelief when handling big creatures in D&D-land. Dragons are magical creatures so whatever. Spiders can get large because somehow their exoskeletons are extraordinarily light-weight (magic or something). But no, I'm not just allowing massive creatures/tanks (even if they hypothetically possess the actual omnidirectional locomotion capacity to move in odd ways...in this case, they don't) to make ridiculous leaps/jumps/parkour nonsense. Not happening. If folks want to have their giants and dinosaurs and other creatures of that ilk doing crazy, square -cube law violating, explosive athletics...sure. You do you. I'm not doing that in my game.
You know, I had skipped the whole jumping bit since it's irrelevant, but I want to point out that what is described here is changing the basic rules of the game in a way that makes melee attackers much, much less effective, and anything that walks (instead of flying or teleporting) noticeably less effective. Part of the balance of a spell like grease is that, if you use the standard rules instead of house-ruling it to be better, almost any creature can easily step over it. I think describing a fire giant or dinosaur stepping over an obstacle that is less than it's stride as 'ridiculous leaps/jumps/parkour nonsense' is completely unfounded. A huge giant crossing 10x10 obstacle is roughly equivalent to a human crossing a 3' obstacle, and for a large creature it's like crossing a 5' obstacle. This isn't some kind of super-parkour, this is taking a slightly long step (huge) or making something that's barely a leap (large).
And discussing the balance of a spell vs a type of creature while house-ruling away the fact that RAW the creatures can easily bypass the spell is silly. Of course if you house rule enough in favor of a particular ability it becomes more powerful, but it's the balance of the house rule that's significant there.
Also, since I'm going on this sidetrack, I'll also say that I find modeling a fast blaster armed hit-and-run walker like the AT-ST with the slow, melee oriented stats of a fire giant a bit peculiar, especially when you're making the walker half the size of the movie walkers (which are around 25' instead of 12'). I'd give them good speed (like a 40-60' move rate, movie AT-ST has a top speed of 55 Mph) with a ranged attack as their main attack.