I imagine that Locust is in actuality Seraphim, now free from Makima's influence and also given a potential power buff now that the concept of Death has been eradicated. Getting a bit into autistic theory here, but Locusts cause the plague, spoil crops and cause famine, all which are things that ordinarily would eventually lead to death if not solved. But if death doesn't exist which in turn means that locusts cannot die, then an individual would have to suffer for eternity the consequences that Locusts bring, an eternal famine, eternal plague, death would have been a mercy that no longer exists. So retroactively, fear of locusts increased, bringing us to now where Seraphim was able to take one of Denji's arms pretty easy. I suspect a number of devils became both significantly stronger and significantly weaker due to the erasure of Death.