Any downshift braking is affecting the rear wheel only. It is also far easier to upset the traction of the rear wheel when downshifting then by using the brakes. As well as the wise words of Keith Code.
I downshift while braking only to have the bike in the correct gear to accelerate. It isn't for any braking advantage. I use my front brakes for stopping (other than trail braking or braking in gravel) - downshiftiing is purely to keep the engine revs where I want them when I hit the gas.
And although I've been riding well over three decades, I'm always willing to learn from someone who knows more than me.
+1 what i was trying to say all along. you are more articulate than I.