Arguably he was; but in precisely the opposite of the way he always ends up accused of it.
You don’t do ‘imperialism’ by drawing the other guy’s continent really small and hurting his feelings; you do ‘imperialism’ by being able to project military force(and maintain supply lines); and then conquering and exploiting the other guy’s continent. A good navigational map is extremely handy for doing that.
As a tool for helping you do that, a Mercator projection is a fine candidate. As a tool for teaching geography, Mercator himself would likely be baffled by your choice(it’s not like he did work on sinusoidal projections because he thought that area was unimportant).