I think post-grad plans are an important consideration, and Brown certainly has a good reputation on the East coast, so that would be something to think about.
I’m not sure I follow your math, or what you are concerned about. You’ll be spending 2.5 years at Brown or Pomona, assuming that you study abroad at Pomona. Not sure this matters. The year at Pitzer and .5 abroad doesn’t really come in to play when you consider your options.