Arman, Gathje, Paddy, Hooker, Charles are all deserving of being up for a vacant title.
They all have something in common:
Arman shit the bed by fucking up his weight cut so bad he had to lie about a back injury. Needs to beat a top contender to get another title shot.
Gaethje is 1-1 in his last 2 with a decision against a year-long post ACL Fiziev (which he could've easily lost) and got body-bagged by Max moving up from FW. Should need to beat a top contender to deserve title shot.
Paddy is on a great streak but has one top 10 win against a very washed Chandler (as great as he looked, Chandler looked terrible). Needs to beat a top contender to deserve a title shot.
Hooker was lucky to get a split vs. Gamrot in a life and death fight and broke his hand so bad it needed multiple surgeries (is going to be out for a while). Needs to recover from his injury and beat a top contender to deserve a title shot.
Oliviera is arguably the most deserving and he's still 2-2 in his last 4, with wins against declined Dariush and decisioning an almost-washed Chandler. Should need to beat a top contender to get another title shot.
Topuria completely unproven at LW (almost got KO'd by a journeyman-style kickboxer in Herbert in his one move up). Should need to beat a top contender to get another title shot.
There shouldn't even be a LW title fight yet, we'd all be fine with two 5-round top contender fights (i.e. Charles vs. Arman + Illia vs. Gaethje, winners fight for the vacant title), but for marketing purposes/to keep the division moving this is what they always do (it's how we got Chandler vs. Charles when Khabib bounced).
The most deserving is Arman, but he can't be trusted with the weight-cut fiasco. The next most deserving is Charles, because his only recent losses are to Arman (split) and the former champ Islam. And the UFC can't risk Topuria losing to a contender after vacating the belt to move up a weight-class, so they kind of have their hand forced to give him the title fight.
Charles vs. Topuria makes the most sense by far out of what options they have on the table.