Just got the last rank of the Armsman perk+Assassin's strike, and I noticed that when i sneak attack it only gives me x15 damage instead of x30. I haven't played Skyrim in a while, but did they patch so we wouldn't be able to do x60 damage?

X15 is what Assassin's Strike gives you. You only get X30 if you are wearing a magic item that doubles sneak attack damage. Armsman has nothing to do with sneak attack multiplier.

Well back in the day Armsmans final perk(the one that gives double damage) used to double the x15 boost for assassin's strike to x30.

But since it apparently doesnt do that anymore. I guess Armsman/Onehanded is useless for dagger stealth builds? I guess I wasted 5 perks.

You double your damage with 5 armsman perk for regular hit as well as sneak hit. You get assassins strike x15 only when you do sneak hit. So you are getting the benefit of both perks, but seeing x15 display when you do sneak hit.

To see 30x display when you sneak hit, you need to wear that DB glove.

Oh, OK. Thank you.