Dr. Strangemonkey said:
It would be because of a number of factors, pikes were also critically important weapons during early gunpowder warfare, indeed the hand firearm was mostly seen as a complement to the pike. Early firearms did have miserable rates of fire, and were extremely inaccurate and unwieldy. This is why the Bayonet charge rules warfare until the civil war.
The question of arming your soldiers with swords and muskets hinged on the expense of doing so, another reason the Swedish army was so sucessful is that the Swedes operated their army under a uniquely cheap economic model that relied a great deal on looting whereas most other countries during this period routinely went bankrupt trying to field large infantry based armies.
And the major complications that result when you have to train men to use and fight with two such complicated weapons as a musket and sword.
Don't be so quick to judge technological superiority the determining force on the battlefield. It's a big advantage, but there are many others that can disrupt its dominance.
Good Point about the Training...okay, so that won't work.
Going back to the question of whether Magic slows down technology, is is possible it could speed it up? For instance, if a mage were to discover that if he had magical crossbow bolts/bullets that spun he'd improve his accuracy with the crossbow/gun, is it possible that engineers might try harder to find a way to do it with mundane technology, and invent the rifled barrel earlier? Scientists throughout history have had to do thought experiments because their ideas were in advance of technology, and simply not possible to do. However, with magic it becomes possible (if not simple). This could lead to practical applications much faster. Magic can create very high temperatures and high currents. This helps Metallurgy in the extraction of ores and creation of alloys. Once Scientific interest kicks in, I'd personally expect things like Aluminium to show up earlier.
Now that I think about it, in fantasy worlds there are some things that have been discovered than they were in our world. And the chief one is Electricity. Someone's going to discover the relationship between Electricity and Magnetism at some point. How long before someone makes the first electric motor (by first motor I mean more along the lines of the Faraday Motor rather than a practical one)? They've got the spectrum of light down, too (well, they have spells that start with
prismatic, so they know you can split light with prisms), so that helps physics along the road to the Electromagnetic spectrum (and in 1st and 2nd edition, they knew about infra-red and ultra-violet too). So even if low technology isn't as good as magic (which I still disagree with. I'll concede on guns vs swords, but point out that swords benefit from metallurgical technology), if they work together, low tech can make way for middle tech a little faster.