I guess Burnes is the most hopeful possible comparison for Sproat, but Burnes at least had a record of success as a bullpen arm before struggling as a big-league starter.
DL Hall is maybe another hopeful example, though his early ineffectiveness was clearly impacted by physical health and maybe the org (or Hall himself) trying too hard to stick to starting.
It's very early to give up on Sproat completely, especially given the physical talent. Right now, the Brewers aren't taking a huge gamble letting him pitch in Triple A or try again out of the pen in mostly meaningless games. But, yeah, last night just went from a potential confidence-boost to total destruction super quickly.
I'd be willing to bet he gets another legit shot next year, with some leash even, but my confidence in his success is not as high as it was with Hall for whatever reason.