This is frustrating, as they are nothing alike, they share as origin the female ruby/sapphire/emerald player/rival character design, but anything else they are widely different as Sapphire is introduced as a cave woman/jungle girl, which focuses on strenght, loves pokemon battles and is in personality way more masculine. A real tomboy so to speak.
It creates confusion in the fandom, which unnecessarly will treat Sapphire as May, instead by their proper name.
It is no problem if the May tag accompanies the Sapphire tag just to see their relation within the subseries.
Just that any future fans don't start mistaking her for the other and the other way around.
That is all.