Of course "Burn Rate" matters.
We're talking about relative burn rates of different powders, and we're talking about 30-30 Win. "Burn Rate", which is a street term of sorts, along with a thousand other variables have something to do with the velocity of a given projectile from a given cartridge through a given barrel length.
Cartridges like 7.62x39 and the new kid of the block, 300 Ham'r, can equal or surpass 30-30 in shorter barrels using faster powders like Accurate 1680 and H300 BLK.
Well anyway, I'm not going to make this into a teaching moment with the 30 pages I would have to write. That's how threads get off topic. Maybe it doesn't matter why most people think powders do what they do in the cartridges they do it in. It could be magic. It could be Satan.
It would be a great topic for another thread. "Relative Quickness" of peak chamber pressure or whatever you want to call it... smokeless powder companies publish relative burn rate charts for a reason. Those charts are more useful to experienced handloaders than the novice.