In the OP’s situation, the only reason I’d leave is if you think the future at B6 is bad.
I got on at Delta at 38 and it’s a great gig but I’ll be retiring at around 2500. That is a bottom feeder wide body guy or a moderately senior narrow body guy.
Joining at 40 today, I bet you won’t crack 3k. That will not get you into the top 10% of most narrowbody A slots.
I’d wager at B6 you’ll have many years in that top 10%.