Lanefan
Victoria Rules
It would be pretty simple to just leave the hard weight limit on spells (i.e. drop the "huge-or-smaller-creature" clause) and not touch grapple.It is odd, in fact. TK can move an object that weighs only up to 1000 pounds, but lets you move a Huge or smaller creature 30' in any direction, even upwards, with no mention of weight. Now I don't know about you, but I would think most Huge creatures are going to weigh several thousand pounds at least. It's like the square cube law doesn't exist in 5e, lol.
OTOH, this is consistent with how grapple forced movement (and forced movement in general in 5e) doesn't care about weights or encumbrance, only size.
EDIT: before someone says "well obviously a DM should just house rule that", the problem is, such a ruling could cause the entire grapple system to fall apart. Let's say an 18 Strength human weighs, oh, I don't know, 190 pounds (a little over 86 kg for non-Imperials). The default carry capacity rules (seen by many as being very generous to begin with) would let this human carry around Strength score x 15 pounds, or 270. With a suit of plate (65 pounds), a shield (6 pounds), a longsword (3 pounds), and a mere 7 pounds of gear, this 18 Strength human would be unable to move his evil doppleganger (created via mirror of opposition) more than 5 feet a turn...except they couldn't even do that, because when trying to move a grappled opponent, your speed is halved!
Then again, if two opponents are each heavier than the other can carry, no problem: they fight in place unless one moves voluntarily. And don't forget you can drag half again your carry cap (at least I think that's still true in 5e), meaning your Str 18 guy could still move his doppleganger at least to a small extent.