Yup, small variations like their voices, skin/hair/eye colors can all add up to meaningful differences. It's not really about any individual customization it's about the sum of all their parts.
Also that illustration is amazing! And supported in lore
"
Devi is a high elf sorceress and the apparent apprentice of Krasus, the alias of the great red dragon Korialstrasz.
She is a dark-skinned elf with raven-black hair, and has both a curious and inquisitive air about her that some within the Kirin Tor's ranks deem impudent. However, Krasus appreciates her up-front nature."
https://wow.gamepedia.com/Devi
So we have evidence of another way to meaningfully differentiate High Elves vs Blood Elves. The skin tones for High Elves (I'm guessing due to the changed environment of where they mainly stayed) can be those similar to Humans. It also gives the vibe of them intermingling with humans as spitefully said by Elisande.
Remember,
Kul'Tirans had the same Human model as Stormwind Humans until they were made playable. And the explanation given was a "sea-faring monster hunting lifestyle".
There's no precedent set forward that a race must stay as how it is when it transitions to becoming playable. In fact the opposite is true, that they get extra customizations they didn't previously have in order to achieve the focused aesthetic differences that Blizzard wants them to have.
So it doesn't matter at all that there is Farstriders existing in the Blood Elf organization. That's not their focused aesthetic Blizzard wants them to have.
Just as it doesn't matter that Stormwind Human sailors/navymen/admirals etc exist, that naval focused aesthetic is given over to Kul'Tirans and made a big show of it. Because again, it's what Blizzard deems is their focused aesthetic.
Same for how a small Night Elf/Highborne mage society exists in Night Elves didn't stop Nightborne from becoming playable.
Just as Alleria calls back to the iconic High Elf Ranger look, that's a focused aesthetic available for playable High Elves to partake in.