Bowser's default size is fairly consistent, but throughout the series his size varies a lot. In many boss battles he's seen as much larger, and in some cases he's Godzilla sized. But there is a reason for this implied heavily throughout the series, which involves what magic/power Bowser is abusing at the time. He's also frequently seen growing in size when involved with Kamek or Kammy. Ridley has no excuse other than inconsistent designs, but he has only minor variations. On the whole, it is shown he is meant to be very large; this is Ridley's natural state, unlike Bowser.
Olimar looks and functions exactly the same. The math is unbelievable, but seeing him interact with the other characters at their level is believable. They can keep everything in proportion for Olimar when he changes size. The same cannot be said for Ridley. Additionally, Olimar has had no interaction with any other characters, ever. His size is only informed, never shown. If the plot were that he was human sized on a macro planet, it would be every bit as believable. Ridley on the other hand has frequent interaction with Samus, giving the viewer a sense of his size compared to human characters.
Anime =/= canon. Charizard's size was established all throughout Smash until his inclusion.