Is this applicable to your model?

https://www.volvocars.com/en-ca/support/man...heel-resistance

I read S60 2019 Early ... I thought earlier car also applied 

I don't know about Volvo but most steering assisted car would assist more when in low speed but reduce steering assist at high speed so that it will feel more steady. This need mecchanic that is familiar with the system.

Another possible common reason is the rear absorber. Have the rear absorber and suspension check. This is something even mechanic overlooked. This is what I'll do first before going into steering assist part like sensor (if there is such sensor).

In the early days of power steering introduction , as similar to pre-power steering days , steering at high speed driving becomes lighter or over-sensitive .

Later days power steering 'technology' has overcome that 'lighter' problem during high speed driving .

I am guessing your 2002 volvo should fall under the latter category of 'not lighter' steering at high speed .

Do you face the phenomenon of uneven tyre wear pattern persistently in this 2002 ?