Logically the tram to Leith should take more buses off streets as current route is duplicated by other modes.
Well, it might actually take the first buses off the street if it's extended to Newhaven, AFAIK the current half-route hasn't taken a single bus off Princes St, the Airlink service still runs as does the Ocean Terminal - Gyle alongside the tramroute service 22.
The buses makes money, the trams don't. Cross subsidies is fine
Lothian Buses capital investment costs are largely new buses though, are they not? They don't pay to build new roads, new junctions and they don't have to directly pay for 100% (or any %?) of the maintenance of the roads they run on. You could argue that LB, or any bus operator, is heavily subsidised by being given so much "free" infrastructure to run on.
The tram is in the unfortunate position of requiring very large up-front capital investment in the routes (at least the tram vehicles themselves have already been bought) before it can even begin to generate revenue.
Lothian Buses invests very heavily in its fleet, it's new, and it's well maintained. A new diesel double-decker costs about £200,000, a hybrid c. £300,000 (and costs for these are part subsidised by Scottish Government grants). Say they buy 10 less hybrid buses a year for 3 years, that's the scale of the tram investment required. Lothian Buses has a fleet size of about 650; 30 buses is not even 5% of the fleet. Perhaps they can suck up 3 years of extra dividend payments by reducing investment in the fleet in the short term? After all, in theory the tram should allow the fleet size to be reduced in the medium term and goodness knows we could do with a few less buses on Leith Walk, Princes St. etc.
All this talk of "gutting" the operator to my ears and mind is just hyperbolic scaremongering driven by an anti-tram sentiment.