Mercedes was supplying engines for McLaren in 2012 and untill 2014. Mercedes had a dog of a car in 2012 and the Daimler share holders were calling to stop the F1 program. McLaren had the fastest car, but unreliable. He left McLaren, because he was fed up with Ron's controlling behaviour, McLaren poor racing management on track and seeming difficulty in beating Red Bul. Self admittedly, Mercedes didn't know where they stood with regards to the output of 2014 PU as they didn't have one reliable PU running for them until 2014! Completely different facts.
Same applies to 2026 PUs. Nobody really knows where each other stands with regards to competitive output of the PUs. Only 2026 will show where RBPT stands.