Great question — answering as the UphillTech team:
This is all very normal, nothing special about it. Some of your assumptions happen to be untrue, and others don't apply to modern ovens. First, temperature fluctuation is the normal way an oven operates. There's nothing wrong with this, it's expected, and recipes work with it. Less fluctuation is better, but you'll never get rid of it entirely, nor do you need to. Second, you seem to be very focused on air temperature. That's only a secondary indicator of a well-working oven. What you need for good baking is good thermal mass. This means that you want to heat up the oven's body, or if it's too flimsy, use additional thermal mass in the form of pizza stones (preferably proper ones), cast...
Full answer by rumtscho: https://cooking.stackexchange.com/a/125104 (CC BY-SA 4.0).
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