Yes. It cooks faster with the fan. Btw, it's also referred to as a "convection" oven as opposed to a "conventional" oven. Air fryers are just small convection ovens.
Actually, air fryers suck in on top of the tray and it comes back from below while a convection oven just creates some turbulences in there.
The difference is that the air fryer removes all the steam that comes off the food, reducing time to crisp up significantly.
That's annoying. If you can't turn the fan off, then I think you need to look for convection oven recipes specifically. But I think they're not too hard to find.
I decided to split the difference and bake my cake at 170, it took half an hour longer than it should to cook and got dried out (i was poking it with a stick every 5 minutes for the last half hour), does that mean 170 in the dial is actually 150?
Tbh, almost all oven thermostats are not accurate for the actual temperature of the oven. Like, they probably are measuring 170 accuretly, but the thermostat is in the very back top corner and the temperature in the middle shelf is 15 degrees off.
People who are keen on baking, roasting meat etc where temperatures are important often recommend getting an oven thermometer so you can see the real temperature.
You're probably gonna have to experiment a bit. For baking and more delicate things probably the listed fan temp, but for things like roasted potatoes it doesn't matter as much.
Honestly, give it a try both ways and see what works better. No two ovens are gonna work exactly the same. I'd start with the lower temp first, and if it's not cooked enough just give it a bit more time and increase the temp next time.
For most recipes (esp convenience food), you just drop the temperature about 20°C and keep the time the same. But in the end, you will have to experiment a bit since every oven is a little bit different.