Hypothetically pay off 2.75% mortgage

I think I came up with one FIRE related situation that might make paying off a mortgage with such a great interest rate actually make sense, but I need a sanity check. Let's assume:

600k left on mortgage @ 2.75%

8k monthly expenses (4k mortgage, 4k everything else)

1.2mil FIRE number without mortgage 2.4mil FIRE number with mortgage

1.2mil to 2.4mil is a big jump and a lot of years working.

Now the hypothetical - doesn't it make sense to pay off the mortgage as soon as you hit 1.8mil and then you are retiring earlier? You don't have to wait until hitting 2.4mil this way and shave off years of work.