Before EW we knew the planet(star) as Hydaelyn not Eitherys, the extreme quests were also written in ARR so it is possible not all details were ironed out back then, planet(star) name being one of those potential things to be added in later as it doesn't conflict with anything else we know now.

As for Hydealyn the primal undoubtedly she fed on aether how much is unknown but we do know she was sustaining the source and the reflections making sure things ran as smoothly as possible, so she certainly wasn't draining too much, perhaps just enough to sustain herself and the power she wanted to trial us with.

My biggest gripe with Hydealyn was she effectively told Minfilia to kill herself for no reason. Hydealyn held enough power to test us which would've been more than enough to speak with us at points she needed to however she told Minfilia to jump into Y'shtola's flow so she can take her aether that comprised her form to speak with us as the Word of the Mother, kinda feels that was unnecessary with the information we have now, so yeah that artwork of the crystal looking like it is binding Minfila of patch 3.2 has worse implications for me now.