FWIW - my last flight, booked as a BA Holiday, got me 13,700 Avios including the holiday bonus.
Given I spent about £1250 total on the flight aspect of the holiday (because when you book flight+car, the pricing is transparent), that would have barely got me half as many Avios if I'd booked it as flight only. Possibly under half in fact, depending on what deductions would have been made for taxes.
All that plus double TPs. Not convinced I'll ever book flight only with BA again...