I really like Banshee, but I was shocked to learn she was at a mere 0.53% usage on last year's published stats. I'm also really fond of Yareli and Gyre.
Not OP but I also used Grendel extensively pre-rework. I think his rework was a massive improvement overall, but he's a different frame now, and not one that stands out to me as much. Being able to suck up an entire room pre-rework just felt great. The new version is an excellent frame that I use a lot, but I feel like the original fantasy isn't all there.
(The rework was totally necessary though. Before it, he only functioned with helminth abilities, which should never be true of any frame.)