I'm not sure if there is scope to change the way efficiency is done but I'll just throw this idea out there anyway..
The main problem I see with the current system is how many games efficiency is calculated over, 30 just doesn't seem like enough. I'm currently averaging 30 games a day, most of these are training but even still I've seen my Eff jump between 30 and 70 in a single day. I just don't see this as an accurate reflection of my actual skill.
This wasn't as much of an issue before but with the new update our ranks are largely tied to our efficiency, so with the current system I am jumping between ranks constantly instead of averaging out at a particular rank. My suggestion is to increase the amount of games it is calculated off to atleast 100. This way players can see where their skill bracket actually is, and as they slowly improve their rank will grow.
Just an idea, id love to know if people agree with me or if I'm out on my own here.