I will say, if I’m Germany, and I see those Russians staying east, I am pretty god damn happy about it. I don’t think there’s any amount of UK air that could delay Germany at that point.
The 18 russians pretty much decide this:
1: Crumple Japan faster, so you can go try to kill monster Germany sooner, but Germany becomes that monster sooner.
2: Try to hold Moscow for an extra two turns so that you have time to crumple Japan before turning to kill Germany.
On the surface, it’s Six one way, Half a dozen the other.
If I see 18 Russians in Bury, I think you’re more than likely coming back to Amur. If you want to convince Japan that you’re going to Moscow, 6 inf need to go to Yakut. And if you do want to go to Moscow, those 6 inf getting there one turn earlier can be the difference between holding Moscow for 2 more turns or losing it.
Keeping the 18 Ruskies in Bury R1 does annoy the hell out of Japan, and indeed the major fear is the dreaded reinforcement of an American landing in Korea. That can be a hard tick to dig back out, and there’s no real way to prevent it, since America is always going to be able to get to SZ 6 since Japan is, and should be, down in the south pacific shutting down UK Pac, taking money islands, and hopefully threatening ANZAC into being more of a turtle instead of a cornered badger. Whether America loses its entire navy to do this and whether they can do anything useful with their stronghold in Korea after they have it, is another story.
The standard J1 opening can’t really “handle” the R2 Amur stack, so that is a decent way to throw a stick into the spokes of the Japanese player. You couldn’t kill what he puts into Manchuria, most likely, but those are units that are never going through China, and you might even be able to tie up a few of his planes for an extended period. Whether or not that’s worth it for the allies, no clue.
Added bonus: The Amur stack usually keeps all of your far east territories yours, so that might save you a few IPCs/round.