This is infuriating not knowing whether daggers are affected by one hand perks or not... never mind whether they are governed by one-hand or sneak (I always assumed one hand...).
It would be very easy to test. It could probably be tested on your first level up. Check the damage on a dagger, invest a perk in armsman and then check the damage again. I just wish I knew
now because I like to plan my builds out in advance.
I worry if they are effected then why use anything else?
There are many reasons. Daggers don't have range, and their "massive" damage would only be on sneak attacks, which you can't really do in open battle. The reason that dagger aficionados are upset is because, as has been said, swords would do more damage than daggers during those sneak attacks if daggers aren't boosted as well. If daggers are boosted, they'll still be outclassed by swords in everything but sneak attacks.