I don't think that's likely to explain jankiness. I do know my way around terminal screens and escape codes, and doing flicker-free, curses-like screen updates works equally well on the regular screen as on the alternate screen, on every terminal I've used.

It's also not a hard problem, and updates are not slow to compute. Text editors have been calculating efficient, incremental terminal updates since 1981 (Gosling Emacs), and they had to optimise better for much slower-drawing terminals, with vastly slower computers for the calculation.