Homebase rule
The homebase rule is a blatant attempt by the ECA at protectionism as it has almost nil effect on larger legacy airlines that employ the majority of their crews at a single hub (who are mostly 'resident' in the country they operate from). The European Regional Airline Association lobbied the EC hard against it but were finally defeated by the unions.
It clearly makes it harder and adds complexity for smaller or airlines that operate from multi-bases (such as your typical loco) employing multiple nationalities.
As a contract pilot the whole concept of paying my social security on 6-9 month contract (in a country where I effectively live in a hotel room paid for by the airline) is flawed, especially as my children/spouse, etc. live in the country where I am ordinarily resident (and benefit from healthcare, schooling, etc.).
As far as I can see the Homebase rule does make some provision for people that have an ‘unstable’ Homebase (I am a contractor working in the airline industry – what is more unstable than that!). I am lucky that the majority of my contracts are run through UK agencies and I insist on staying in the UK social security system for any short-term contract work and ask them to apply for an A1 form.