The many stupid fetch / kill quests and graphical bugs alone are enough reason to rate it below 90. A good RPG has meaningful things to do that are not arbitrarily thrown as mandatory tasks between story progression. WoW style kill 5 XXX and fetch 10 YYY quests are not state of the art anymore but Xenoblade has hundreds of them.
The original Xenoblade Chronicles had the same problem and most Let's players on youtube just skipped the boring sidequest stuff. And the balancing was another problem, if you did the side quests you were overleveled and if you skipped them you were underleveled and had to grind, especially before the endboss. But despite all these problems Xenoblade was still the best JRPG released within the last 10 years because all other aspects of the game were close to perfection.