The price of the camera is not 80% sensor and 20% everything else. IBIS unit, EVF, Digic, memory, readers, LCD and materials for the body, projected volume (economy of scale) - return on investment ...
Thare is a reason for R6 and not wrongly projected supply of sensors. In first year you sell the sensor at the premium with the premium package (body, readers, EVF) all the while perfecting any problems in production (it is easear with a smaller production volume). With the R6 Canon may have also bridged a year of problems with supply chains and scaling of production BSI stacked sensors while making a big profit selling a very competitive body. And maybe good sale numbers of R6 just opened a new strategy resulting in a similar move for R6 II.
So the R6 II price is not than unusual - they can reuse the R6 body, maybe older DIGIC from the R6 and not the advanced one from R3 with less cache memory resulting in 20fps (not 30fps of R3), lower quality EVF (R6 could use an update - in low light it lacks dynamic range), dual SD is cheaper ... and you have a very, very capable body that is very competitive in the market and is a viable choice for all the people who cannot afford or justified the price of R3 or as a second body with similar specs. And you have R3 as a premium product for all the people who needs it.