Is there a benefit to adjusting the difficulty every so often (ie 2 weeks) vs adjusting the difficulty every block?
In brief with hindsight: It's a mistake.
You have to keep in mind that Bitcoin is the very first Cryptocurrency. It has all the legacy designs and did not anticipate every possible problem. This includes the block-size, which initiated the huge Bitcoin 2x fork debate.
And btw, it's not every 2 weeks. Bitcoin has no means of calculating time accurately other than blocks. It's every 2016 blocks, and if we say every block is 10 minutes on average, 2016*10=20160 minutes, which is 2 weeks.
Newer tech, like Ethereum and Monero adjust the block-time dynamically. For example, Monero decides the difficulty as an average of the last 100 blocks.
Yes, there is a risk with adjusting the difficulty every block. It entirely depends on the method of adjusting. With how Bitcoin does it, if you adjusted every block, the difficulty would vary wildly due to the variance in times between blocks. However other algorithms for determining the difficulty may be able to account for that.
Adjusting every 2 weeks allows for the average time between blocks to be close to the actual time between blocks (by the law of large numbers) so that the adjustment can happen without being effected by the variance in times between blocks. The method used by Satoshi is very simple and straightforward with its effects easy to see and model.
Like almost every other "magic number" used in Bitcoin, the 2 week interval appears to simply be an arbitrary number with no real reasoning behind it.
2 weeks is a time which is enough long and enough short at the same time, guarantees a fair weighted balance between diff target recalculation and possible diff based attacks to the network.