The limiting factor for most turbine engines isn’t really operating hours, but “cycles”, which is to say starts and stops. From a maintenance perspective it’s not terribly important whether you start the engine at the gate or the runway.

Also, as far as maintenance goes, engine hours are weighted by operating power. So, an hour at idle doesn’t count as much as an hour at cruise power. One of the reasons airlines started using not-full power on takeoff when conditions allow it is because of “power by the hour” maintenance contracts, which incentivize that.