Elemental Adept isn't supposed to be good or strong. Its not a feat 99% of spellcasters will take, nor should it be
Its a feat designed specifically and exclusively to elevate the sub-optimal, but popular playstyle of the dedicated elemental caster. It succeeds at that task well enough so...
....Which is a way the rules could have been written. Instead of clearly saying "make a ruling on what makes sense", they give a convoluted procedure that when applied literally does not work.
Has the original SA Compendium been removed from the D&D Website???
Looks like the old Errata docs have also been converted from downloaded PDFs to dndbeyond webpages only.
For 1st printing runs of a large RPG, the amount in here is honestly less than expected. 2014 D&D, pathfinder 2e, call of cthulhu, Edge of the Empire, Runequest - all of these have a similar or greater amount of errata items picked up after first printing.