There's just not a closer, which is also why they haven't felt the need to overpay for one. Even Kimbrel wouldn't have closed as much as he did, his preference aside, had Alvarado not been hurt (and to a lesser extent, Seranthony also struggling).
Hoffman's good with men on base which Alvarado probably isn't. They are both good over multiple innings (if not necessarily long outings). I think if anything Kerkering is the guy who can earn his share of saves if he outperforms Seranthony.
Don't know that I agree about Covey though. If he fills his role or makes a few decent spot starts that's more than enough. Any game he enters in April is a game that's already gone badly (or the bullpen in general has). And it's not even certain he makes the team.
Rather than closing, the role is high-leverage, and that's where we know for certain Alvarado is the #1, but we don't know who the next RHP is at #2. And if the situation calls for Alvarado to get some big outs against a LHB in the 6th or 7th, that will put Soto or Strahm in play for the 8th or 9th if it happens again.