If he's in the low 90's now, that's a positive sign. Could've sworn I read an article last week about him peaking at 90 though. Could be based on what game was seen though.
I'm hopeful for Estevez but I don't believe he's our #4 arm in the organization. Purke, Meyer, Ray, Solis, and Rosenbaum for sure. But there are guys with better stuff(although maybe no the results yet) that would be viewed higher. Guys like Turnbull, Demny, maybe even Karns and Smoker because of their power arsenal. Taylor Jordan as well once he's healthy.
There's a lot to like about Estevez so far but I don't think he's a great prospect just yet.
Estevez and Ray are debatable. Both are young and projectable Ray is a lefty but Estevez is a bit younger. So I can see putting Ray ahead of Estevez the other guys you mentioned not so much. Smoker and Karns are relievers I'll rank a young, projectable starter over a reliever any day especially Smoker he's still living off his stuff and draft position results so far have left much to be desired. Solis was drafted and noted as an injury risk and his two trips to the DL thus far have done little to get rid of those concerns. Turnbull is 2+ years older than Estevez with a limited track record. Demny is a solid arm but I'm more of an Estevez fan.