That would be the case were it not for the fact they don't...

That would be the case were it not for the fact they don't actually have a usable network without TPG's fibre, renders your whole point null and void, VHA have large legacy costs and no fibre, whatever price VHA can put forward TPG can match but make double the margin.
TPG will keep slowly growing number as always due to the cost advantage they will always have, this is the model they have used to grow since inception and will continue to use, the only time growth accelerates is when they buy out a competitor.
Only thing stopping them from being able to challenge TLS directly are VHA's assets, now ask yourself again, why have TPG not built over (duplicated) any of VHA's network?