Is it Bash beats Power Attack, Power Attack beats Block, and Block beats Normal Attack?

How do I deal with magic-based characters?

How should I handle when I am surrounded and can not block everybody?

I always follow the advice of an accomplished Bosmer swordswoman:
"When confronted with a wizard, close the distance and hit 'im hard."

Bash the enemy then attack and repeat.

Against mages you need magical damage reducing effects, like enchantments, standing stones and racial resistances.

And don't get yourself surrounded. Try to keep the enemy in bottlenecks.

Dabble a bit in magic yourself. Restoration is *AWESOME* for melee for two reasons: Ward and Respite.

Ward gives you a shield that fully blocks magicka (up to a point, when the shield breaks) and doesn't slow you to walk speed allowing you to close the distance on squishy mages.

Respite is an augmentation of health-healing spells that also additionally replenishes your stamina. Which means more power attacks and shield bashing.

There's a block?

The only advice you need is to stick them with the pointy end.