It's showing that my minimal on-road biking for the past 18 months has definitely degraded my bike balance and thus ability to hold a GOOD line. Can i hold a line enough to get by in a race - sure, just did a sprint tri with a busy multiloop course no problem. Does it mean I"d trust myself if things got dicey or supercrowded or if I even hit a slick? Nowhere near as much as I'd trust myself if I were roller-capable.

You can obviously hold 'a line' if you can't ride rollers, but you'll hold that line much more cleanly and reliably if you're roller-capable.

And no, riding rollers doesn't replace on-road practice for cornering, etc. Still got to do that as well, working on that one once the late spring hits.