I see what you mean, but I'm not sure I agree.
Onoki only makes Ay super heavy
at the moment of impact. He does this to maximize both speed and power. So, basically, Onoki makes Ay super light, Ay uses his amped light-weight Shunshin to gain massive speed, and at the last second right before impact (or perhaps even at the moment of impact, kinda like he does
here), he makes Ay super heavy in order to maximize his punching power. This strategy maximizes both aspects responsible for producing Force, which are mass and acceleration.
Low-key, it's insane that Tsunade's still stronger than an Ay who's amped by such a degree, she really is HER.
The same result would not be achieved if Ay was being made heavy the whole way, or even half of the way to his target, as that would likely massively hamper his speed, which we know is
a major contributing factor behind his punching power.
So, in short, Ay is only made super heavy at around the moment of impact. Him getting to Madara would still be under the effects of lightened mode (We literally see him using his Shunshin on his way to Madara), so getting heavy at the last second wouldn't really affect his overall speed in that moment, meaning everything I said for Tsunade would still stand.