Rubick: 1 Spell Steal Build

Has this build been brought up before? Me and my friends are currently testing this build out, and our verdict seems to be 'good idea' so far.

Basically, Rubick gets Spell Steal at lvl 6... and will not bother to level it up until 14. Or maybe until 24. Instead, he will get level 2 Null Field (assuming you max Tele first) by level 11.

The logic of this build is thus:

1. Leveling up Spell Steal only grants you larger margin of error (longer duration and shorter cooldown) instead of actually raising its effectiveness. In other words, "If level 1 Spell Steal is just as effective as level 2, why bother raising it?"

2. In a purely mathematical sense, raising Spell Steal from lvl 1 to 2 increases its duration by 33% and reduces its cooldown by 10%. If you choose to level Null Field instead, that's a 100% increase in effectiveness from 5% to 10% (although actual resistance will be less than this, I know).

3. In a practical sense, it is no use holding on to that stolen spell for too long. Let's assume you managed to steal Ravage with its 150 second cooldown with lvl 3 Spell Steal, and used it. Are you really going to hold on to that Ravage on cooldown for teamfights? I personally think it's better to ditch it and grab a more practical spell for teamfight such as Ice Path (which is incredibly OP it's unbelievable) or Wraithfire Blast. As well, once it's off cooldown, can you actually guarantee a teamfight will happen within the next 150 seconds? If you can't, then you have just held on to that Ravage for nothing.


Thoughts? Suggestions?

*Additional thoughts:
Since this idea builds on the fact that Spell Steal's effectiveness remains the same regardless of level, a possible solution is to add differing effectiveness of Spell Steal depending on level. A possible idea (although this may be broken / unbalanced, suggestions welcome):

Lvl 1 Spell Steal: Rubick will have to cast using the caster's cast animation time (no instant cast).
Lvl 2 Spell Steal: Rubick will cast using his default cast animation (instant!)
Lvl 3 Spell Steal: Able to steal Aghanim upgrade, even if he does not have Agh himself (back to pre-patch 6.79)

I agree. It forces you to move to the next spell that could be of use. The only thing is you don't have to think large with rubick. Smaller spells with shorter cool downs could do the trick in a team fight/ganking. I like stealing lock downs myself.