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Is it possible to achieve, retain and make use of CR1/IR1 visas while staying outside the US, but working for US companies as an employee, paying US taxes, Social Security, etc?
No, it is not possible. An immigrant visa itself does not grant you any rights you're looking for, such as a right to be employed in the USA. You get those rights by entering the USA, turning on your immigrant visa and paperwork and - assuming you're admitted - receiving the conditional/permanent resident status. This status is what essentially grants you those rights.
Then you can apply for employment in a specific company, and after some time ask to be moved abroad on a temporary assignment (which can last a while). This way you'd be considered an employee, and eligible for employee benefits - many of which, such as US health insurance or FSA plans, would make no sense for you anyway.
The catch, of course, is that to keep this status, you have to be physically present in the USA 180+ days in each year, which you don't want to do. Thus this will not work for you.
Finally, to work for an US company from abroad you do not need any kind of US visa; you either work on a contract basis, or are hired by a local office of this company, if any. As you already mentioned, you would get more limited opportunities, but this is not because you're not American. The USA-based job market protections do not apply in this case, so you're effectively competing with people from other countries, many of whom have low salary expectations.