Lower temp can only be viable if you reduce the work needed to run the engine, and can still output the needed work/energy.
This is related to why work and heat are both measured in joules.
Gas burns at a much higher energy than steam, so it's much easier to extract more energy with less fuel, making for a smaller form factor.
I should clarify I was talking about an engine here. Not a power generator.
What I said is correct though. You can compensate for lower temperatures with a more efficient engine & energy conversion, and of course more fuel/input.
The actually relevant distinction is that gas turbines, like other internal combustion engines, have a much higher ramp rate than external-combustion engines like a steam turbine. This makes “peaker” gas turbines a crucial resource for establishing power grid stability.
To get energy from heat, you need a hot end and a cold end. The more difference between the two, the more energy you can extract. Extracting energy from small temperature differences is very inefficient. Temperature is measured from absolute zero for this.