How to describe useless comments

Solution 1:

prosaic could be used as a "nice" way to say uninspired. Indeed, it may possibly be taken as a compliment (see 1a below).

From Merriam-Webster:

Definition of prosaic
1a: characteristic of prose as distinguished from poetry : FACTUAL
b: DULL, UNIMAGINATIVE
prosaic advice
2: EVERYDAY, ORDINARY
heroic characters wasted in prosaic lives
— Kirkus Reviews

Solution 2:

An idiom applicable here is separating the wheat from the chaff. Cambridge Dictionary:

to separate things or people that are of high quality or ability from those that are not:

Literally it refers to the processes of threshing and winnowing to separate individual grains from husks. The metaphor for separating things of value from other items entered English from the Bible, including Matthew 3:12 (KJV):

Whose fan is in his hand, and he will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire.

In Middle English, the Nun's Priest's Tale by Chaucer gives one version of the resulting doctrine (3441-3443):

For Seint Paul seith that al that writen is,

To oure doctrine it is ywrite, ywis;

Taketh the fruyt, and lat the chaf be stille.

(For Saint Paul says that all that is written is written for teaching us, indeed; take the fruit and let the chaff be still.)

So in your example, most comments are chaff, but there is a bit of wheat among them.