Even with Grayson, there is a significant chance he never establishes himself as a solid starting pitcher or that it takes a few years to get there. Prospects are volatile. Especially pitching prospects who have a much higher risk of a major injury which dramatically changes their abilities.
Just picking a random year, in 2016 3 SP were in the top-10 having reached upper levels of the minors (Rodriguez is currently #8 according to MLB). Lucas Giolito, Alex Reyes, and Tyler Glasnow. Glasnow and Giolito are pitching well as SP this season. So that's encouraging. Reyes is a RP, but is pitching well. But the road to this point was very volatile for each. Reyes had lots of injuries and only pitched 72 innings total from 2016 and 2020 and he's only a RP. Glasnow and Gioltio both struggled for multiple years (5+ ERA in 200/240 IP from '16-'18) and got traded before putting things together. Both have been good since 2019. Glasnow has had stronger performance (2.80 to 3.50 ERA) but Giolito has had better health and availability (400 to 200 IP).
2016 would be equivalent to 2022 for Rodriguez. So while it's certainly possible he hits the ground running, I think expecting him to be pitching 180 IP at a mid-3s ERA next year or in 2023 is a bit optimistic.