Why not double check your math.
A larger bucket (like a garbage can) will give you a more accurate reading.
Perhaps the flow restrictors are removed from the fixtures? 4 GPM is not a lot if your worried about flow rates down the drain and 4GPM is a lot if you are wanting lots of water. I would not freak out over these numbers.
When flow rates get over 12-14 GPM you need to make sure the drain can handle it. Over 16-18 GPM and head water build up over the drains grate can measure as high as 1/2" in my private testing.