I get the feeling the Austrian TLD is still mismanaged. You can’t even have it on route53 unless they finally added support. I’m assuming that’s not an accident.
I don't think .at is mismanaged, quite the opposite, but in the way of many ccTLDs it is a little bit eccentric. I don't know why route53 might not support them: perhaps it's to do with contractual faff, or possibly because nic.at uses a less common flavour of EPP.
(Sadly the common flavour of EPP has a bonkers data model; a few ccTLDs use an alternative model with a more sensible data model, but although the more sensible flavour of EPP is easier to use in isolation, it has the downside of being different from the ICANN flavour.)
(Sadly the common flavour of EPP has a bonkers data model; a few ccTLDs use an alternative model with a more sensible data model, but although the more sensible flavour of EPP is easier to use in isolation, it has the downside of being different from the ICANN flavour.)