Personally, I don't think you comparing apples with apples here. Renault was just a supplier like Mercedes was to Mclaren before they entered the fray, they would have been happy with either winning. This is the silver arrows we talking about here, a fully fledged works team with only one goal in sight, to win. Considering all the resources ploughed into this project, you'd be naive expecting Williams or any other customer team to receive equal support or HP for that matter.
Sorry, but you're wrong here.
Renault entered into a partnership with Williams when they returned in 1989. They also contributed significantly to Williams' budget. It was a full works effort and Williams got the engines for free!
It took political influence/interference before Renault would supply engines to Ligier in 1992 and those were a step behind in specification. Even with the possibility of Alain Prost driving for them! And Ligier had to pay for them (more than 25% of its entire budget).
In 1995, Benetton got the Renault contract from Ligier (which had been acquired by Flavio Briatore to that end) and managed to convince Renault to give them equal engines as they had the reigning worldchampion (Schumacher) and would pay for the privilege while Williams still got them for free....
And McLaren's original deal with Mercedes was also far more than just an engine supply. Mercedes eventually acquired shares in the team and bought the full livery rights in 1997 so they could turn McLaren into silver arrows....That's far more involvement than just providing engines.....