You can delegate authentication via a permanent DNS record to another DNS hierarchy and give your certificate software authority to change that for ACME purposes. This fixes both the "My API key is allowed to change anything" problem and the "I can't get an API key for the DNS domains I need certificates for" problem, albeit at the cost of needing that one-time setup to tell ACME where to look in DNS.

To do this you need a CNAME from the _acme_challenge DNS name you're being challenged on, to a DNS name you're going to use for this purpose. It needn't be in the same domain or indeed even the same TLD but of course it does need to be a public DNS name.