I always worry about teams that are ultimately controlled by bean counters and this will always be the case when the team is owned by a major manufacturer (other than Fiat / Ferrari).
Recent history has only fuelled my concerns - Honda, Toyota, BMW
F1 teams have to have access to finance quickly, so they can react to situations as they arise. Big Corporates like gradual, planned, justified expense.
I can't see Mercedes giving Ross enough freedom to compete with McLaren, Red Bull, Ferrari and with lack of suitable freedom they could quickly come under threat from Sauber, Williams, etc.
I deliberately avoid commenting on Lotus because I really do not understand the ownership. Renaults involvement has always impressed me. For a company that stuggles to sell cars anywhere other than France, their commitment to Motor Sport is spectacular - just witness a World Renault Series event and you can't help but be impressed.