Sorry but you just didn't inform yourself. The dimensions for the luggage are very clearly stated. Nowadays I would expect it to be common knowledge that when flying with a budget airline you have to pay attention to your luggage size and should have the boarding ticket QR code ready. For a small effort you get a small price.
Not really, with a little discipline it can work for the vast majority of scenarios. 90% of my flights are backpack only and that includes travel where I needed to be dressed formally and travel with my SO. The only scenarios where it's actually necessary I see is if you need health equipment (which most people don't), if you have toddlers (which I'd argue you shouldn't be flying with anyways), and if you are moving a lot of stuff (where paying for luggage is still cheaper than shipping in many cases).
It just requires a little planning which I think most people my generation and younger are getting used to.
