They have Boyd, Imanaga, Taillon, Horton and Rea that can pencil in as your MLB caliber SP. That's 5 right there without counting Steele eventually coming back. Rea is probably not what you want taking every 5th spot in the rotation, but he is capable of giving you league average production in that spot. They still have Brown, Wicks and Assad. They don't need to start the season with another starter. They could potentially wait it out with what they have and then decide at the trade deadline who is worth giving key starts to this potential and likely playoff team.
Not saying they should do that, but I wouldn't rule it out that it's what their thinking. Make a run at a guy like Imai and if they don't like the price tag, sit back and wait for the right deal or wait until the trade deadline. This team is likely giving a run for the division as is. How it looks come playoff time could be different and should be different if they are serious about winning.