Enduser, as I said before, foregoing insulation is both inefficient, and, because it causes weatherproofing to be especially difficult, it makes the oven potentially dangerous.
There are a lot of insulationless/chimneyless oven designs floating around, but
1. Have you seen the pizzas that come from them?
2. Do the owners of these ovens continue to post about their experience with them after one or two uses?
Anyone can build a pile of bricks, make one or two less than mediocre pizzas, let the elements trash the oven and then lose interest, never to post again. The common denominator for all these uninformed builds is embarrassingly bad pizza and an incredibly short public record.
Additional concerns like insulation and chimneys are a bit of a pain in the butt, but, at the end of the day, you've got a piece of equipment that cost you a few hundred dollars that can produce a similar caliber of pizza to a $10,000+ Neapolitan oven.
Even a pile of bricks is going to take a considerable amount of time and money to put together. If you're going to invest that much time and money, you might as well put in a bit more and end up with an oven that can make truly wonderful pizza and that lasts more than year.