i recently did this, it did not look great, and it took a month to grow back.
my advice? you’ll need to draw them on every day while they’re shaved, so try drawing them on the way they’ll need to be and see if it looks the way you want it to.
if it looks good, and you’re sure you’re up to drawing them on every day, what i did was find where the brow curves down. don’t shave half your brow off, just make a sort of straight line from the inner edge of your brow to the outer edge, so you can keep as much brow as possible, then use a brow razor (not a body shaver, not a tweezer) from the outside inwards on every hair beneath that line. your undrawn brow will still have the arch, and then taper down for about a cm or so if they’re like mine, but the bottom will be straight and you can fill in up and out until it looks right.
but be sure you want to do this before you pull out that razor.
maybe your lashes are super healthy and strong? idk. sounds genetic to me. have you tried heated lash curlers? that might hold a little longer.