Don't have one if they're not useful to you.
We don't have an oven any more, we find the combination of microwave, drawer style air fryer and bucket style air fryer/slow cooker does all we need.
If it's not cooking things, that's either you not understanding how to use it - for example, putting things in inside a dish that stops air flowing around it or overcrowding it, or say, putting in a huge raw spud and expecting it to cook the inside at the same time as the outside (you would need to use smaller spuds or microwave them a bit first so the inside has a head start).
If you can't cook fish fingers in under 45 minutes... are you putting them in a dish that blocks air flow?
Or, it's defective and not actually reaching the temperature it says it is - which can happen with budget models.
We regularly do baked spuds, chips, wedges, breaded/battered frozen things - in our Ninja two drawer job. It doesn't take as long to reach temp as the electric fan oven used to and cooks those things a bit quicker.
That's not why we have it though, we have it so we can use all our workspace for whatever we want, bringing out whichever appliance we want to use, and because we're using less power to cook things as it is more efficient.
Do you not think that all the people saying theirs are great, and you, the minority saying based on a tiny handful of experiences, that they are crap... might suggest you're incorrect here? That you or your air fryer are the outlier, the anomaly?