Mercedes is McLaren they are the largest share holder 
That is correct. And when eventually Mercedes owns all of McLaren, what will happen next? Mercedes like Toyota, Honda, BMW (Its German rival), Renault and Ferrari are want to going to race as themselves. Ie
MERCEDES, not McLAREN-MERCEDES. Also when they win races, for the constructors point of you, Mercedes are going to want to her the "
Lied von Deutschland" not "God Save the Queen". This is a fact. Germans want German domination. The only way to achieve this is to when Mercedes fully aquires McLaren, to rename the team to Mercedes and then get a
German racing licence instead of a British one. The team would likely still remaing Woking based however. This is what happened to Benetton when it ws aquired by Renault. Team is renamed to Renault, a French licence replaces the Italian one from old team Benetton, but team remains British based. Same is the case with BMW. Sauber is Swiss and team still based in Switzerland, but team nationality (BMW) is German as they have a German racing licenece. The same example can also be given with Honda based also in Britain and Toyota which is based in Germany. Both team nationalities are Japanese.