Magic damage vs Physical damage based on level

Having read various threads and discussions (both here and on other sites) I'm wondering how to effectively play as an offensive mage (note that I do not mean a mage who goes around offending people).

It would seem that while base damage increases with every skill level for physical attacks, the only way to increase base damage for offensive spells is to...buy stronger spells?

Since I don't have access to them until I a) level up quite a bit, b) I actually find someone who sells the specific spells I want and c) can afford to buy them, how do I keep my destruction spells from becoming useless when my physical attacks are constantly getting stronger?

Even the upgraded spells don't seem to make up the damage difference by the time I get them (e.g. Firebolt is 25 dmg vs base Fire which is 8/sec).

Am I missing something about how to effectively use destruction magic in the game? Is it currently not worth focusing on being a mage? (that last question is a bit subjective so feel free to ignore it)

You are 100% correct in your misgivings. Due to destruction magic not scaling, you will lag behind in terms of damage done late game (especially if you up the difficulty). The only way you can make up for this is via the enchanting perks that lower destruction magic costs so you can cast and spam more spells. If you can get it down to 10% or less cost via multiple enchanted items, it is still viable due to the fact that you have instant stagger at your beck and call with the dual casting and impact perks, not to mention heavy aoe with fireball and such.

If you don't mind modding, there are already mods out there that improves destruction magic.

Finally, you'll still need a backup plan in case you run into some highly magic resistant foes (Breton with dragonskin activated, for instance.)

On the other side of the equation, while physical attacks get more powerful, the armor they must overcome also gets more powerful. Magic resistances stay flat.

Don't forget about resistance poisons for a bit of extra kick.

You are forgetting about Alchemy. If you get Alchemy to level 100 and couple that with Enchanting level 100 with all your gear increased with Fortify Alchemy, than you can craft a Super Fortify Destruction potion, giving you a total of 150% Damage increase! Plus the 50% from perks, you're talking a 200% total damage increase.

Incinerate 60 damage one-hand, add the 50% perk bonus, 90 damage one-hand, now add 150% to that, 225 Damage one-hand, now with two-hands its 2x the Damage totaling 450! But that's not all, now add the Impact perk which adds another 20% for a grand total of... 540 Damage per blast! Not to mention the Stagger from Impact, I do say destruction completely has physical damage beat!

These are all great points, but I would like to add a tip to your magic user. You could add some Sneak skill and Illusion skill to make a rather deadly mage, remember that an attack while hidden doubles damage, unless it's magick-based I made a lightning sniper, using the silent casting perk and invisibility spell with illusion. Additionally, a good Sneak skill to help avoid detection. Using the theoretical damage of 540 as mentioned before, double that to 1080 (that's without criting mind you), then consider that certain lightning spells have incredible range and accuracy, coupled with silent casting you could take down a large group outdoors without ever being detected. Happy hunting :D

Resists are flat and my only problem with killing any enemy has ever been mana. Skyrims mobs scale with your level and most of the time if you have problem killing its because you're working trade skills too much early pumping your levels up too quick for the damage you can output with the magic. Do this - All Destro magic until you can't place points. Anytime you can't put a skillup on that put it on alteration first, resto second. (you'll see why in a second). Alteration gets game breaking paralyze and that changes everything without how hard it is for you to win. 1200 weapon hits are powerful, but considering the damage shields and being armor capped as a mage you aren't too worried about them. If you allow your destro to lag then you have problems at all levels -- it is your top priority skill followed by alter for the protection/para. Spend points on mana until you have 250 base and then spend heavily on health -- you actually can rock more health and have as much armor as any melee class albiet with a spell. Work your trade skill points in only when you can buy nothing in other areas (mid-high level). At that point you want to enchant your armor for dest and alteration since these are the spells you cast the most you should be casting mana free except for conj and resto -- resto is already terribly efficient and I wouldn't waste the enchants on it as one double cast fast heal can nearly fill your health bar.

At low level do the mage college quests to get the mask and arcane mage robes they will allow you to continue with the insanity until you reach high level. ;)

Oh yeah.. pump fire and lightning first... fire deals with all undead and nords... lightning for enemy casters of all races. Use cold on argonians, dark elfs, brentons.