No, there are no "different levels of assimilation", by definition.
Language is a basic requirement for integration, by the way, way before assimilation.
I think your last sentence misses the point that there is no obligation to accept immigrants and that the host country is sovereignly free to accept or reject anyone they wish.
Thats what OP was saying though, if countries want assimilation to that high of a degree, they should encode it in a law. Otherwise, they are being duplicitous by inviting skilled workers on one hand and then creating structures which drive them away.
For example, there can be a legal requirement to have a B2 level of German within 3 years of being in country, if the requirement is so important.
Right now, the policies say one thing and politics say another.
P.S. : the real reason such a law would never exist is because it would drive a huge amount of skilled immigration away and this is something also politicians cannot afford.
Language is a basic requirement for integration, by the way, way before assimilation.
I think your last sentence misses the point that there is no obligation to accept immigrants and that the host country is sovereignly free to accept or reject anyone they wish.