Not to sound like a wet blanket, but all these idea's are potentially game breaking if applied to NM's. And SE doesn't particularly like us breaking NM's, so don't expect any of them to work on NMs. Like I've said in previous threads, make simple things, the more simple it is, the less variables and factors involved, then less room SE has to screw it up.
I agree with simpler math reduces the chances of programming errors. I also agree with TP moves can't be stopped (though Paralyze can stop TP moves).

Though, there are examples of spells out there that other classes have access to that act as speed bumps for the foe when building their next TP move. One example is Absorb-TP. It damages the target's current TP and gives the caster an equal value of TP to the caster. So, asking for a TP hindering/damaging move is not too far left field to request for. The math can be made pretty simple.

Yes, I have suggested a spell that might seem game breaking: Sadness. So, If you don't mind, saevel, I would like to see how you can make this spell idea fit into what your view would be a proper spell to cast on an NM.
Spell: Sadness
Element: Water
Magic Type: Black
Skill: Enfeebling
Maximum duration: :30 earth minute
Cost: ~40 MP
Method of Removal: Erase
Description: Under Sadness, the target will not be able to gain TP at a normal rate. Instead the rate of TP the target will be able to gain will be half. The duration is based on the caster's INT versus the target's magic defense.
The mentality I was going under was short, intense enfeebles. Your view could be what can balance it out. I am curious to see what you have to suggest. I look forward to your response, if you chose to participate.