While he would have slightly less service time than right now, historic evidence (meaning last year) also shows that it is possible for the market for starting pitching at the trade deadline to go quite out-of-whack, with way more demand than supply.
Last year's deadline is a perfect example, and take a look at the White Sox. Lance Lynn was leading the league in HR given up, had 2 months of control, and was owed like $7 million for those 2 months. The Dodgers gave up their 8th best prospect for him, and took on Joe Kelly as a gamble because why not.
Giolito was being inconsistent, slightly better than 2022 but you could still see the issues if you did some scouting, Lopez was generally bad to open the year in the bullpen, but the Angels gave up a top 100 prospect for him and Lopez.
The Mets gave up Verlander and Scherzer and got back guys who are now their top 2 prospects, + more. Yes, they had to send along some money with them, but both were having injury issues and teams just took chances on them.
If Cease struggles like he did last year, then the odds are his value isn't lower at the deadline than it is right now. He is still a strikeout pitcher with high level stuff. Teams will take a chance on the ability to fix him, figuring that the White Sox's pitching coach is trash.They might not give up the asking price right now, but his value won't go down just because of the lower service time.
Cease's stuff last year was iffy, he put up an ERA of 8 in August, but was pretty good in September. There have been hints that there were mechanical issues last year, so it is possible that this is fixable also. The White Sox should have changed pitching coaches, but too late for that, so we hope for the best. If Cease is just normal next year, slightly better than his truly weak 2023, then he will go into the deadline with an ERA in the mid 3's, with 1.5 years of control, a high K rate (teams like this for the playoffs) and a salary affordable to everyone. That might well be the most valuable player to move at the deadline.
The only real downside risk is injury. While this is a real concern, Dylan Cease is also a guy you might gamble on. He has been the most reliable starter in baseball starting in 2021. Maybe that just means the injury is coming, but if you're going to gamble on a guy being healthy, better to bet on Cease than on a guy like Kopech who has been a mess of injuries the last 3 years.
This was all pretty obvious at the start of the offseason. Cease struggled last year, the struggles were real, and this would likely matter to teams. Plus, compared to the deadline last year, there was a lot more pitching available for teams to spend FA dollars on, so the market was much less constrained at the deadline. The White Sox didn't need to be in a rush to move him, they could hold out to see if someone really wanted him or became desperate. If no one became desperate, they can hold him to the deadline this year with hopefully limited risk. Sitting there with a high but plausible price, seeing if anyone met it, but not being surprised if no one did was always the smartest and most likely path.