so I'm an L21 orc dual-weilding fighter, cruising merrily along, and when I enter the cave to get Queen Freydis' sword I pretty quickly get _pounded_ by a swarm of conjurers with their flame atronachs and fireballs. My follower is Erandur, BTW.

any tips on best tactics? I've found that even using the Orc 'power' AND shouts, I still lose.

Archery works for me when I keep taking a beating , pick them off from a distance . It helps if you put enough perks into the skill tree to get the slow time perk . Make yourself a fortify archery ring too . It's actually not a bad idea to enchant a bunch of rings and amulets with fortify archery , one handed , two handed , etc . They weigh next to nothing , and can give you that life saving damage boost when you need it .

Drink a fire resist potion and kill the conjurers as fast as you can. Ignore the atronachs

the whilwind sprint can get you up close so that you can express your displeasure in a more personal manner.

I found that when I am faced with a tough opponent, a Paralyzing potion (either on bow or blade) the 2nd time around will do wonders and gives me the few seconds I need to finish them.
The other posters mentioned some great tactics as well - Whirlwind Sprint is a good idea, resist fire potion, resist magic potion, and drink a HP potion when you are low on Health, it doesn't hurt the combat if you stop it to go to your inventory (better to pause and heal, than to drink healing potions and still get bombarded by spells).

If you have a summon scroll or spell or staff - use it! Even the odds. I really like my Senguine Rose staff.

Oh I had another idea, when I see that I'm facing a lot of opponents, I point my staff into the room and summon my dremora to take the heat of me and to cause a distraction.

I do what MBP does. My bow (Deadric upgraded to Legendary with smithing at 100) does 173 damage. They go down from a distance with just one shot. Pick them off one at a time. Piece of cake.

Get yourself a follower to take some of the heat off of you. There are several that can be hired without any addition quest requirements...maybe win a fist fight, etc. Equip them with decent armor and weapons and let them take the brunt of the punishment.

OP is level 21, doubt he has a Legendary Deadric bow! LOL My Daedric Bow does over 200+ damage (with 40% Archery ring and Archery at 90) plus my sneak is at 85. So yea, I just look at these clowns and they fall over dead! hahahahaha

But yea, at lower levels, just use summons and shouts and followers and potions to even the odds!

scroll of summon atronach
scroll of mass paralysis
scroll of fireball

it's easy to forget about the scrolls you may have picked up in your travels, now is the time to get them out. as mentioned, don't forget about your shouts. being a dual wielder, if you are using un-enchanted weapons, elemental fury would make quick work of everything in the room....including your follower. LOL