Okay, I’m just gonna get down and dirty with this scene for a moment. This is the perfect example of why Penny is “smart” enough for Sheldon. Penny and Sheldon come from two very different points of view. Sheldon is an analytical thinker and has a scientific mind. Penny runs on intuition and her social intelligence to maneuver through the world. Where Sheldon lacks, Penny thrives and vice versa. I hate seeing people say that Sheldon has to “dumb down” things for Penny. Do people not realize that Sheldon operates on a different plane of existence? He is speaking a language the rest of the world - even his fellow scientists don’t maneuver in their day to day lives (and I’m not just saying that - I’m a scientist and know a lot of scientists both personally and professionally). When Sheldon gets on his high horse, Penny is easily there to show him the real world holes in his thinking. Where Sheldon is there to point out to Penny other variables and alternatives she hasn’t considered. They compliment and compensate for each other in more ways than one, and that’s why when you see them in action together, they become this unstoppable, functional unit.
Penny doesn’t need to be academically as smart as Sheldon because that isn’t a challenge to him. Sheldon respects that kind of intelligence. However, he still is in his own little bubble about other ways to appreciate a person for their own talents and strengths. And that’s where his interactions with Penny become such areas for character growth with him. He is faced with this person he would never initially consider or value but she proves time and time again that she is not only someone of worth but challenges him in all the ways he hadn’t thought of before.
The thing is is that Sheldon doesn’t make Penny feel stupid. Leonard does. Leonard excels in the real world applications that Penny as well thrives along with being an intelligent academic. But when Penny is around Sheldon - it doesn’t matter that his IQ is 187 and he has a theoretical understanding of the workings of the universe. Because he won’t think that he can get soup delivered, and she’s there to point out the obvious. Penny knows where her strengths are with Sheldon and she blossoms in them. Where Leonard makes her feel entirely uneasy about her own security (not necessarily intentionally though he does have his own ways of picking at that wound over and over and over again for her).
Basically what I’m saying is it’s horseshit that anyone thinks Penny and Sheldon aren’t equals. You can’t measure them against each other because they approach the same problems from entirely different world views. They’re opposites through proximity and circumstance and found each other.