I'm not so sure I get this reasoning, of course it's great to have diverse subject matter, but if your raps are whack, then what you're trying to say will never resonate with anyone. This applies to ALL kinds of rappers, not just street rappers, so I don't get why you would only care about the level of lyrcism that comes from street rappers, and not rappers like Cube.
As for the last part, I think that you're severely underrating Prodigy here. If you were talking about his performance on The Infamous, I can somewhat agree to him being on even footing with Cube in terms of lyricism, because whether you realise it or not, P and Cube have the same approach to rap, more focus on having a dope delivery and straight forward lyrics without getting too metaphorical or abstract.
But if we're talking Hell On Earth P onwards, I'd have to vehemently disagree. Apostles Warning and Still Shining are just two examples of Prodigy getting metaphorical as hell. Prodigy is better with imagery than Cube, as you can see on Get Dealt With. P in his prime was cranking out quotables like motherfukker, that's why he's one of the more sampled artists in rap.
The only things I will say that Cube has over P in spades is more diverse subject matter, and depth. That's why I can agree with the last part here, but I thinlk that you're severely underrating Prodigy as a lyricist, he's a lot closer to Cube than you think.
When did I knock Cube for not being lyrical?

I know that you don't have to be lyrically complex to make dope music. It's all about using whatever skills you have to bring something to the table, and Cube did that and then some.