I honestly have no idea what the google apps offer that windows 3rd party apps+Microsoft apps don't offer.
I guess the want for google apps is so that people on android or ios using google apps won't have to switch to new apps. But the thing is, google apps are not coming unless W10M grows ALOT and if Windows phone grows alot without google apps, then everybody will be using the Microsoft apps that they've been using forever back when google apps weren't available and google apps will just not even be needed anymore.
So essentially google apps only matter if they come while W10M is an infant, because if W10M grows up without google apps into an adult then it will no longer need the google apps as it will be perfectly fine with the MS apps it has grown with since the beginning.