Good question, but I dont think the Jays took him in rule 5 with the goal of making him a pen arm, but ratyer they knew they had to put him there in 2026 to build up his innings and thats really the only place he could be for an entire season.
With the ability to option him as of next season, my guess is they stick him in Buffalo as a starter and see how the arm holds up with a starters workload and be in the 6-8 range on the SP depth chart.
Ponce isnt fighting for a spot, he's one of their top 5 assuming his knee is healthy.
Arrighetti is probably the defacto #5 right now with Bloss, Estrada, Dallas, Van Eyk etc fighting for depth relevance along with any other offseason acquisitions.
Bowden Francis had TJ in Feb so his recovery would put him on track to return at some point. Berrios as well though he's likely after the AS break given his May surgery