My 7in was way to light with a 5000mah Li-ion battery so I doubled its capacity and that was helpful. I plan to add another 5000mah (total would be 15000mah Li-ion pack) to see how she flys.
Its not that your quad is too light but rather lighter than most standard builds, because of that it will require more tuning.From what I understand
My typical build plan is to select and purchase the battery last after planning the build with eCalc and then buy a battery after construction that gives me the thrust/weight I want. Or really it’s the Throttle Linear @ Hover I use as the reference.