Linden Greensitt you are wrong , people have not been allowed to work in spain of any kind from the uk after brexit. The visas state that,that is now different though.
And you will be able to work without having to proove that a spanish person cant be employed as it was before.you were not allowed to work here before on a nl visa now after just 12 months you could.
With regards to the double rule, will that really affect that many people? if you have an income from pension or rents then the double ruling doesn't apply. But what if you have 40K in savings you have passed the 27K barrier you get your visa what are you going to live on for the next 4 years? 54K is a decent level to sustain you over the 4 year period. Anything less and you will struggle without an income (which isn't affected by the double ruling.)
People have always been able to work or become self employed once they have arrived in Spain, it is quite common for people to arrive (especially those intending to become self employed) and then apply for a SE visa (having arrived on a NLV), the same goes for people looking for work you dont need to wait until the end of the year you can apply at any time! OR are you saying that after 1 year you can work or become s/employed on a NLV?