First of all, this is wrong: "The whole purpose of FP was to avoid standing in rides and to be able to ride more rides."
That might be the purpose for YOU, but the reason, and ONLY reason WDW has ever had for the fastpass system is to distribute riders through the park at peak hours and to make sure that people are spending money in the parks rather than waiting in lines...It has NOTHING to do with being able to ride more rides. That's been your perk, but not the reason they exist.
As to "eating up your battery life" checking fastpasses -- either a) people have poor memories, or b) you should get a different phone that has a better battery life if checking it once or twice is going to eat up your battery. It takes seconds to do that, so exaggerating that isn't going to be helpful to anyone looking for answers here.
I've used the Fastpass+ system on three or four trips now -- and it works great. It is true that those who primarily go to the parks to ride all the rides are going to have some lines to wait in. It is also true that for the vast majority of visitors its going to make life very easy. You can plan in advance - or not -- you can change your reservations and fastpass times on the fly throughout the day -- and for the vast majority of visitors, three fastpasses is probably all they will use. As a season pass holder myself, I used three fastpasses each day, but I programmed them in the morning, based on what my plans looked like. Anyone who knows the park system knows that you do not need fastpasses first thing in the morning or during EMH -- do the headliners then, and save the fastpasses for your second park if you parkhop, or not. You can plan three fastpasses for MK, for example, not use use them in the morning, and completely delete them and select three fastpasses in a different park in the afternoon, for example.
I think the primary people who will be complaining about this is not going to be the regular park goer -- its going to be the teens that run from ride to ride and ignore the rest of the parks' activities, shows, and dining. To them, I say, I get you. It IS going to be different from hereon out.
Based on last weeks visit, it looks like they are just about ready to completely turn it over -- don't be surprised if this happens in the next couple of weeks.