You sound emotionally weary, so there's an argument that the best thing for you is to leave Meta — not necessarily because it's the best path for your career, but it's sounding like the best path to helping you feel reinvigorated about your career. There's a lot to be said for feeling better about something, regardless of whether that thing is the optimal for you career-wise.

One question is whether getting to IC6 is a prerequisite for your happiness. Realize that companies like Microsoft and Meta view IC5 as a reasonable "career-long level" — meaning even lifelong IC5's, if they're solid, are well-appreciated on most teams. If getting to IC6 is necessary for you to be happy, then a hard, honest assessment by someone with full context about your realistic ability to get there will help. The rest of this answer is premised on the assumption you have the skills and abilities to reach IC6.

Here are steel-man arguments that would make each of your options hypothetically the best one:

• Keep pursuing IC6 on the same team. You have a great manager who supports you and has high confidence you'll reach IC6. You are respected on the team and your context makes you much more effective than newer IC5s. The team works in the area you're most excited about in the whole company. What the team needs most are exactly the skills you have.

• Change teams within Meta. You like the mission and benefits of Meta, but things in the previous paragraph aren't true. You have learned how to operate differentially well within the culture of Meta relative to how you'd operate elsewhere.

• Move out of Meta. You have an offer with a company which you are more aligned with mission-wise or culturally. Your skillset is a great fit with what your new team needs. The size of the new company is well-matched with the size of company you do best at. You're so discouraged at Meta that any change would feel welcome regardless of outcome.

At the highest level of abstraction:

• Don't make your happiness contingent on something you can't control. This, for instance, is why I recommend an objective outside assessment as to whether you have what it takes to get to IC6.

• There are many less-competitive companies which would happily give you a Staff Engineer title today. In fact, the weaker the company, the more they'll be willing to throw out all sorts of titles and levels. Is it really the IC6 itself that matters? Or is it something else you're trying to get?

• Sometimes we change because we know exactly what's wrong. Other times we change because we can't figure out what's wrong, but suspect that continuing isn't going to improve things. Both are fine reasons to, especially if you're not risk-averse.

My intuition is that you submitted this question because you're already emotionally ready to move on from Meta, and that you'd be happier doing so regardless of outcome. But the ultimate choice will come from you deeply introspecting to figure out whether that's indeed right for you.