Kind of, I'm not sure if I entirely understand what you're saying.

The 50 applicants will not be objectively better or worse than the current 400, but somewhere in between. If you are adding 50 extra people, chances are there are going to be some in those 50 that have different life stories, experiences etc. that WILL out compete people who would otherwise get a position.

Last year, say 400 applications and 100 are admitted (25% acceptance rate). If 50 additional people apply, Successful applicant number xx-100 in your case probably wouldn't be receiving a spot because some portion of the additional 50 people applying will likely be getting a spot.

Also imagine a school where 150 people apply for 100 spots, versus 100 people apply for 25 spots... which is harder to get in? I'm mainly thinking "competitive" as what stats (GPA, MCAT etc.) and what EC would let you be admitted...