What drives a poor reputation for the Rogue class?

[KorvinStarmast]

And since this is a level 9 party, we're at a point where the opposition that might actually worry a competent party (especially if it's for more than a week) is stuff like illithids and archmages and angels and such. And the competition for your job is something like an Eloquence Bard.

Or a whispers bard.
As to the Rogue/Assassin feature at level 9 ... perhaps add
"You can cast the spell nondetection once per long rest without using spell components" as a part of that level 9 feature.
Chances to infiltrate suddenly expand and the spell caster in the party isn't taxed.

Non detection lasts for 8 hours. If you wanted to scale it down as being "too powerful" then have it last one hour, like Freedom of Movement and some other buffs.
Spell durations tend to be instantaneous, 1 minute, 10 minutes, 1 hour, 8 hours, 24 hours, or until dispelled.

As compared to a different martial benefit: Level 10 barbarian, Totem, gets Commune with Nature as a ritual, and that's a 5th level spell.

I know it's not at all germane to the issue, but I do find it slightly vexing comparing assassin against subclasses published after WotC threw their hands up in the air and decided to embrace power creep with clear eyes and open hearts. Most 2014 subclass options are bad compared to 2020 or later subclasses.

The power Creep in Tasha's was marked. There was a slight power creep in Xanathar's, which in some cases they could have mitigated by (for example) back filling "always known ranger spells" for the Hunter and Beast master...but they were too lazy to do that.