The 3 degree powered approach has become a standard arising from many years of experience. Any skilfull pilot will readily recognise a small deviation from 3 degrees and endeavour to regain that angle. It sets up a pilot with a standard view of a runway and an established expectation of all of those intuitive/trained control inputs to achieve a smooth touchdown and rollout.
The only acceptable variation should be related to terrain clearance during an instrument approach. Can't think of a good reason for having an approach angle less than 3 degrees unless it relates to spool up time for particular engines.