Why are people discussing roamer as if he's an entirely different class from pocket? They're both soldiers, only with different jobs that are entirely dictated by the meta-game and has nothing to do with "balance" as such. You could run two shotgun pocket soldiers just fine if you wanted to, but every team chooses not to since that would leave virtually no heals for the demo and scouts. The medic can only heal a certain amount per minute, and the answer that people have developed over time is to have one of their soldiers play away from the combo, relying on med-kits and (usually) make use of the gunboats.
The meta-game is constantly shifting as people adjust to new strategies and further refine their play, and right now the roamer just so happens to generally play a style that involves going for " big plays," bombs and distraction plays, but there's no telling what will happen over time as people become better at the game, come up with new strategies and new maps are introduced.
I think it's important to realise that the roamer's currently "weak" position is entirely our own construct and that you are free to change his role into something that you feel would make him more useful (say, leave him far back and only use him to spam until the ubers get exchanged at which point he jumps in and helps the combo, or whatever. You can literally do whatever you want as long as your team is willing to go along with you).
The roamer is not weak. He's just a second soldier whose life we decide to make more difficult because we believe it helps the team win.