When Shakespeare wrote: "When sorrows come, they come not single spies, but in battalions", why didn't he put an "as" before "single spies"?
In this sort of context, where the nominal is a secondary subject complement, EME did not require as with nominals, just as we still don't require it with adjectivals:
He came galumphing back.
He came home defeated.
Here's a non-Shakespearean example:
Firſt, [God] comes a Little-One : to ſshew, that hee is food for Little-Ones ; [...] A little One hee comes, from the leaſt of the cities ; Little, of Accompt : Little, in Appearance ; that we might not be afraid to come neere him. [...] And laſtly, he comes a Little-One to us, to ſhew, we muſt come, as Little-Ones, to him. —Austin, Devotionis Augustinianae Flamma, 1635
So Shakespeare might include as or omit it; and the meter here calls for omission.
Mainly to maintain metre, but perhaps also to make it a metaphor rather than a simile. The metaphor sounds more arrogant, more assertive, which matches Claudius' character.