The best way to see how shit Mori is, is by comparing her to Amelia. Amelia is a shy holo with bad social skills, it tends to take time for her to learn to vibe with another holo's personality, and if she doesn't know them well she often creates awkward moments through non-responses OR stilted/slow responses (as if it takes too long for her to figure out what she's "supposed" to say) when set up for a comedic moment by her collab partner, if she doesn't know them well.

She is in many ways similar to Mori in this way. However, you can tell just by watching most of her collabs that she's trying to get better at it AND is actually doing so. Her recent collabs are much better than older ones. And she becomes much better if she knows their personality. So clearly it is just a matter of practice for her.

Contrast this with Mori. She has been the same since debut. Nothing about her has changed. Every collab is just "yeaah" "that's right" "naruhodo nee" spam from her regardless of partner. Even bots can hold better converations. There is zero indication that she's improving at it, as the Coco collab shows.
Worse yet, she is virtually the same with people she knows well. So scrap the "it's because of shyness!" cope, because that's obviously not the reason. She got her bully "gimmick" with the chicken and yet still, most of the actual conversations go the same way as with anyone else. The awful Shadowverse duel is a great example. She literally doesn't fucking talk for 90% of the collab and then is just like "Tehee sorry Deadbeats your boy was very focused on the game but I promise I had fun and wasn't salty from losing 5 times in a row!"
She doesn't even feel bad about delivering such an awful performance, and that's why she, unlike Amelia, doesn't improve.