its not about the second season not deserving to exist. i mean. i can understand why people dislike it (its my less fav part) because its completely different from the first 25 ep (=7 volumes in manga).
l's death was necessary, but SPOILER WARNING AHEAD OF LAST EPISODE:
light's death too (and that could only have been done with season 2). underrated opinion but the anime represents death note SO BADLYYYY.
dont get me wrong, i dont dislike the second part, its just not my favorite one, but after reading the manga i learned to love it and, to be honest it has good character devlopments too so, give it a try cause its not that bad, its just different and bad-adapted in the anime