All heroes are viable in pub dota, its strictly a matter of recognizing which team comp has a better late game and if you don't you have to push, gank, and be aggressive. If you have the better lategame, you need to retain map control and farm farm farm.
Some 5 man stacks we played with in the FoH channel, Me (very high) + varied skill (normal to high) We ended up against PL both games (of course) and won both. Simple things like 5 carries v a team with teamfight is a hard game to ever win unless the teamfight team doesn't push. In low tier dota 9/10 teams with the advantage don't push. So many low skill games end up with the early game team getting way ahead, farming for a year, and then lose late to a team with 2-4 carries on it because they just didn't push.
If you and your friends are all close in relative skill, ability to farm and control the map is virtually a wash. At that point it does come down to the meta game aspects of pushing, defending, punishing the opposing teams heroes that can beat you based on game duration as much as anything else.