Well, in Yasim, EGT starts at 20F or something stupid like that with idle engines, it's very unrealistic. JSBs isn't much better,
I suspect it's unreasonable to expect instrument readings etc. from the generic systems to come out okay. If you have a notion of what this should read for your particular engine/use case, it's easy to make an <fcs_function> in JSBSim or an equivalent property rule that produces your reading.
So yes, JSBSim is much better because it natively comes with the tools to simulate whatever system you need to a near arbitrary amount of detail - including engines and flight dynamics. No one is forcing you to use the generic stuff.
Focus on FDM-type things which you can't address otherwise, not on things which are best fine-tuned aircraft-side.