To sum it up, I'm surprised how much of a challenge I'm having with the last few forts/dungeons I've attempted to clear. And forget about trolls with their health regen mechanic -- I can't draw and shoot arrows fast enough to outpace their hp regen. I don't mean this as a complaint post at all, I'm just wondering if there's something I should be doing differently to improve.

I'm on my third toon (playing on Master), a sneaky archer type who has aspirations to become a dagger assassain, but whose 1h skill isn't high enough yet to pull that off. As a result, I spend an inordinate amount of time whittling mob health down, one arrow-from-hiding at a time. Any bandit type higher than a basic Bandit requires a surprising number of shots, all from stealth, to take down. If stealth gets broken, it's almost not worth fighting anymore -- half the time I just reload rather than attempt to chip away at hp so slowly. Perhaps my issue is with archery instead of sneak per se? While sneaking, archery seems to do avg at best dmg and outside of sneaking it does almost nothing at all (my stats below). Anyone else experience this?

My basic stats:
Level 20
Sneak 75 (perked)
Archery 50 (perked)
1h 35 (no perks)
Gear is average at best at this point

I think part of the problem might be that sneak leveled so much more quickly than my direct-combat skills that perhaps I've level scaled myself right out of the competition, so to speak. I changed from thief to warrior stone when sneak was at about 45 and I realized how quickly it was going up.

Part of the problem is maybe my gear, which I haven't improved via smithing at all.

And of course, Master means that even basic mobs have a large pool of health, but I have a hard time believing that this is all due to Master.

The first half of a master playthrough is very very hard. Find better arrows and or bow, or just set the game to expert for a few levels.

At the risk of stating the obvious, twice, bow with fire enchantment, v. trolls, and maybe buy some archery training to get it nearer your sneak for a few levels..

I could definitely use a solid bow upgrade, but I'm determined not to make my own gear this playthrough (already have a dual-wield warrior that I'm making my "godmode" toon). I'm only using an ancient nord bow right now, if memory serves.

Is 45-50ish archery low or average for a level 20 character?

I'm too stubborn to turn difficulty down to expert, for better or worse. Maybe I'll grind up enchanting a bit (no perks) and thrown on some +archery dmg enchants. I'm desperately trying to make a powerful-but-not-broken toon this time, so I'll probably have to ditch that gear pretty quickly, eh?

Snipers are sudden death if you have the right gear. Try to get items which gives a bonus to Archery and use the best bow you can get. Join the Dark Brotherhood and/or Thieves Guild for the best gear. Add Illusion to your build because things can and will go wrong and that's your ticket out of it. Being able to turn invisible at will or calm the meanest Draugr Overlord is a life saver. Make sure you take the Marksman perk in the Sneak tree for 3x damage with bows.

By Level 26 my sneaky archer was maxed in Archery and had all the perks except for Steady Hand which I have no interest in. I also take the sneak perks just to get the x3 damage. I've come to the conclusion that you probably have to do some smithing to your bow to get the damage up to some acceptable level. By about Level 40 on that character I'm feeling underpowered even with an Ebony bow with fire or shock on it. I don't see any way around improving your own weapons to keep pace with the enemies. Maybe someone will come in and tell me different; I'd love to hear how. I'm not too excited about smithing, but I think it might be necessary.

For your position now I'd suggest getting a ranged weapons follower to tag along with you for backup. I travel with Marcurio, the mage from the Bee and Barb in Riften. His sneaking is superior, he rarely breaks out of sneak before I am detected and I can take him through a room with me that has enemies in it and unless they run into him they don't detect him. I take his dagger away so he is all ranged all the time. He has a bow and uses destruction magic and is very effective. There are other followers I tried, like Jenassa, who is a ranger, but her following wasn't as robust as Marcurio's. She got lost a lot more often and didn't stick as close to me. Marcurio doesn't separate from me as easily.

If you don't have the Power Shot perk I'd recommend it. Staggering enemies is very, very helpful and when you get to the top of the tree, that last perk, with paralyze is great, and helpful as well, especially with bosses as you tend to put a lot of arrows into them and the chance to paralzye is 15%.

Oh, and if you are perking and using Archery you should find archery improving gear in the world. Or at least I have. Both in chests and for sale.

I see no benefits to playing on Master; especially against human(oid)s. The way Bethesda implements its difficulty levels is crude and human(oids) can take freakish amounts of damage and survive. I always play at one level below the hardest difficulty because of it. I wish they would implement a difficulty system in which we could make creatures as difficult as possible and human(oids) less so. Being able to turn a human into a pincushion and have him still fighting just freaks me out (In FO3 the equivalent was several bullets to the head. Freaky).

Keep it on Master, you will get there. To state the obvious, you need more bow damage. So, better bow, better arrows, +Archery items.

Something that might help, in degrees of spoilerage from one to three.

Getting Faendal as a follower early on helps, as you can get archery training from him. Later on, you can look up Aela the Hunter (one of the Companions). As others have already mentioned, doing some Smithing will greatly improve your damage potential. And try to move on to higher damage arrows. Hopefully you are not still using Iron Arrows at 20 ...