Chainring teeth divided by cog teeth gives you a power factor. If your largest cogs are the same you'd be getting something like 18% less low gear power from the compact double.

My 35 lb hybrid had a 28/34=0.82 low gear ratio. On my 23 lb triple road bike my lowest is 30/27=1.11 I could climb almost anything on that hybrid, even with the weight penalty.