I don't think Gill does balance that equation because he doesn't provide them with powerful ball running either.
But this starting back row of Quirk/Schatz/Gill was never about having a big bopper to crash it up.
The young, fleet of foot trio would tire the opposition out disrupting their ball and give security to the Reds, then you'd have Horwill and one or two of the front rowers crashing it up before going second channel and letting them run wide or unders back through a tired inside defense who couldn't realign.
In that mix you also have Gill who has a deft pair of hands and plays the #8 role on attack as far as link work goes. In contact he's a bit like Michael Hooper for mine - somehow manages to break tackles despite not being 120kg. He plays heavy because he has great balance.
Beau is a fine player when it comes to being an utter prick at the breakdown, but doesn't have the hands or skills in contact that Gill does. Once you break up that original trio, its no surprise that the other two start to look a bit lost. Throw in the fact that Genia's service is a bit off and the gears are missing every now and then, putting more pressure on everyone - snowball.
EDIT: and if the defence was a bit too good first up, then the Reds would go to plan B: kick for territory, let Simmons pressure the opposition lineout (apparently) and let the fast backrow force the opposition into an exit strategy they didn't want.
I remember that game at Suncorp against the Chiefs where, early in the second half, the Reds' pick and drive game was executed at such speed that the visitors could not align. They expected the Reds to go wide, and committed few in the zero channel, so the Reds PnD'd about 40 metres, sucked in all the forwards, and two passes later were in on the tram tracks.