I looked at Jamis some time ago, I wish they made a Coda with a chromoly fork and disc brakes.
Stupid marketing...
The listed specs for the frames are
Coda Sport:
Size Specific Design Double-butted chromoly frame, extended head tube with reinforced collars, double tapered cromo stays, forged dropouts and fender/rack eyelets
Coda Comp:
Size Specific Design Disc Brake Reynolds 520 double-butted chromoly main tubes, extended head tube with reinforced collars, double tapered cromo stays, forged dropouts and fender/rack eyelets
They are verbally identical except that Coda Comp lists Reynolds 520 tubing vs. generic chromoly tubing for Coda Sport.
However, Reynolds 520 IS chromoly (not heat treated):
Cycle Tubing & Tube Sets - Reynolds Technology (heat treated is Reynolds 725, Tange Prestige etc.). Given that both Sport and Comp model are made at the same facility (Maxway Ltd.?), what are the differences? Maybe tubing profile (both are double butted anyway) or seamed vs. seamless. Since both frames use "size specific design" and the same alloy, who on Earth knows the specifics?
I would say get the higer model if you want a carbon fork and disc brakes. Speaking of the compliance of the steel frame, a non-disc fork can in principle be made more compliant.
IMO some components on these bikes are a shame. How about a square taper crankset (fc-m371) on a $820 FX3 disc? Even better, Octalink fc-t4010 on a $980 Coda Elite? Why not T4060 with an outboard bottom bracket?
Have you looked into drop bar bikes? Gravel bikes are essentially drop bar hybrids. Something like Jamis Renegade or Double Cross? It will cost a bit more, but it will probably be better suited for more riding. You can keep the MTB you have for beach rides and some more relaxed riding.
An hybrid is essentially a rigid MTB with slightly narrower tires.