i would not say it is the best in the franchise but it definitely among the best. but it definitely has the best world building in the series.
people should not divide things with mmorpg vs single player since the storyline content is rival single rpg content out there despite having mmo label. it is unfair tu push the game aside just due to the genre labels without properly giving it proper chances. the game developed as final fantasy rpg foremost with mmo multiplayer second and majority portion of the game is single player content. for mmo it surely it has the best story but saying it only has the best story among MMORPG is doing the game massive disservice as it its content quality also among the best in rpg in general. ofcourse, people would be very sceptical hearing this but those who actually play the game know the depth truth of this matter. i too used to be in that position until i play it by myself.
and when people praise it, people speak about on expansion onward. the base game A Realm Reborn indeed suffer from slog, bloated quest and pace issue. those who tried the game but cant get passed ARR and yet baffled at how people can praise the game is because those people did manage to pass the base game ARR and experienced expansions onward content. most of players acknowledge and agree ARR is slog and the good stuff in Heavensward onwards.
sure, it has advantages of continuous story being told non stop compared to single big game as how tv series vs movie are but due to this it has great amount character development and world building. saying it has quantity advantages over qualities also a big lie.
obviously some people has different preferences which is understandable but majority reception toward the game storyline is really good even from rpg perspective. only minority speak otherwise.
Shadowbringer's writer Natsuko Ishikawa even received
standing ovation during 2019 Pax West.
also Hironobu Sakaguchi currently very enjoyed it, finished whole game in merely a month, Heavensward in 2 days(without sleep) amidst with his daughter wedding while Shadowbringers around 3 days. thats gonna speaks about something.
Yasumi Matsuno also just finished second playthrough with his public character.