This is an insane q, but I have to at least ask....

No. It's too likely to be really patchy.

It's also a reeeeally bad idea on the scalp. If you end up rubbing it into the roots, you'll rub it on to the scalp and almost certainly get chemical burns. A friend of mind did it. It was ugly! (And very painful for her!)

Having said that. When my hair has been longer, I've done root areas with a brush and then down the hair slapped it on with my fingers. It's a lot quicker, but uses a lot more bleach.

When I do a bleach bath I never use a tint brush. For me the advantage of the bleach bath is that the shampoo makes it so much easier to apply than just bleach. I just squidge it in with my gloved hands after sectioning my hair into quarters. I am really generous with the product, and everything gets covered. It is the only way I can do my whole head by myself, even putting a semi on takes me over an hour, I have a lot of hair.
If you want to make sure you get even coverage, i would try doing it in two goes, instead of trying to do your whole head in one go. So section off the top half and bleach the bottom half, then do the top after the first lot of bleach is rinsed off. Make sure you use the same bleach/peroxide ratio and keep a record of the time you leave it on for so you can replicate it and get the same result. (Dont do the left side and then the right, just in case lol)

I do my bleach baths the same kinda way as Wicked Pixie. Section into quarters, but then I'll divvy the quadrant up into a couple/few sections and just slap it on with my hands + run it down each section so it's evenly covered. I think the main thing doing it that way is to make sure you're getting all those hairs in the middle of the section so it doesn't come out patchy or having chunks barely lifted. That's why I divide each quadrant up.

Since your hair is so long though, you may still need to divide it up and do half at a time. Ideally it should take you no more than 15 minutes to get it on. So if you're doing it and it's taking longer, just stop where you're at and just deal with what's already covered and move onto the rest when that part is all processed and rinsed

Omg it takes soooo long! 🙁  Yea when I do roots I use the tint brush and I'm careful but for the lengths, ugh. I'd probably do them first and then attempt the top if need be, because the ends are so much darker. But yea, I figured. Btw,  the word "squidge" is the best lol.  I also recently heard that using an old synthetic foundation brush is easier for roots than tint brush which picks up all those little fly aways. Gonna try that.