Even putting aside the fact that Eclipsa has shown no interest in retaking the throne (and in fact her gleefully giving up the throne is how this whole ordeal got started), as well as the fact that her only heir is a destructive manbaby retard right now:
The "Festivian" line of queens has existed and ruled Mewni for 300 years and has almost definitely married and mixed genes with other royalty in the past (most recent example being, obviously, Moon with a Johansen prince). We have no idea how many Butterfly queens there have been, but given there are 11 Festivian Butterfly heirs including Star, they might actually outnumber the queens from the "original" line. There's no evidence at all that there's any difference between the first queen's possession of the wand and any random woman's possession of the wand: magical powers, cheek marks, and even the Butterfly form, which is almost definitely where the surname came from in the first place, all stem from the wand. Meaning that the first queen was a "peasant" as well before she received it from Glossaryck or out of the ether from the Realm of Magic or whatever.
Star has literal royal blood even ignoring the Butterflys, Star owns the wand and has been physically shaped by magic itself, she's genetically related to a line of women who themselves were shaped by magic, she's descended from the family who's held the throne for literal centuries, she's not a fucking retard with rage laying waste to the countryside because she wants MOMMY GIB THRONE. Star wins.
It feels like the fandom is hyperfixating on the current Butterflys not being "real royalty" when if anything this plotline is just drawing focus to the arbitrary nature of it all. There is no difference between Star and Eclipsa beyond who they're very distantly related to (in both cases, some rando girl given the wand and "becoming" a Butterfly that way). Even Star isn't focusing on it beyond the initial revelation.