Maybe, leaning towards it tbh.
By portrayal, he probably was a top tier or at least low top tier in his prime, as a (seemingly) DF-less normal human character.
Roger - peak top tier
prime Rayleigh - high top tier
If Gaban was the old gen monster trio, then:
prime Gaban - mid top tier or at least low top tier
A character cannot reach this level without either advanced conqueror's haki, or a top tier DF, at least as per current precedence.