Coal and wood fired ovens usually have a huge thermal mass so once it's up to temperature with a particular size fire it will stay there.
Edit: the gas oven doesn't predate the thermometer, but traditionally is set by "gas mark" rather than a thermostat. Old recipies would say "gas mark 7" etc.
Having said that, gas ovens are a pain to use until you've got used to the one you've got. I've never had one where the actual temperature of the oven matched the gas mark it was set to. Typically you'll have to benchmark it with an oven thermometer and then adjust whatever the recipe says to fit.
Gas hobs however, you can take from my cold dead hands. I'd rather use a camp stove than an electric hob. Nothing beats instantaneous heat adjustments.
You can get that with a good induction stove. I still prefer gas, but induction is pretty good. Other advantages of gas are for example the ability to use non-flat pots (woks or similar). On the other hand it's much harder to clean.