Thing about using the frame data the way you are is that you're not accounting for how much dash JC <action> and dash SH aerial store the momentum from the dash, nor the actual placement of the attack's hitboxes within the move.
To understand this, just dash JC grab and then dash JC u-smash. Aim for the fastest JC after dash possible. They both have the same speed but you'll notice he slides forward more from the grab than the u-smash. So u-smash out of dash JC actually has less reach than grab. Neat. Now compare if you do dash SH nair, aiming to jump as soon as you can out of your dash. Now compare that to the other two. Again, another unique reach.
Also I have no idea how you got u-smash being 4 frames faster than nair. Nair takes like 7 to come out, after factoring for his jump startup (jump start is 3, nair hits on frame 4). His u-smash hits 7, but you have to JC into it and it starts around his feet so it's really hitting with the hitbox that's active on frame 9 (without factoring in the JC). So really it's more like frame 10-11, provided I did the math correctly.
I maintain b-throw and then just tech chasing him or accepting that you've made Falcon DI away and tech roll to the edge, placing them in a very dangerous place where they can die for no reason at all and can't really dash dance anymore is actually pretty good. But then the catch is you have to be decent at edgeguarding, gimping, and handling pressured he-men.