If leaving after 4 months to a new place is going to make you a more happier and productive employee, I say go for it. At 4 months, your airline has gotten their monies worth out of you already.

If you are worried about what other airlines are going to think, I wouldn't. The pilot shortage is just getting started and won't even reach its peak of destruction for several more years.

There is going to be plenty of job hopping in the near future, unfortunately most of the hopping pilots won't have the choice as 2 or 3 airlines are certainly going to fail this year and into next year.