No, they did not get better. That is how they perform. This is also typical behavior when using a cell at near or over its rating…any cell.
A big issue is that ultra-high capacity batteries have high internal resistance. That causes a lot of voltage sag so you reach the low voltage cutoff of your ESC sooner. This voltage sag can easily wipe out any advantage in capacity the 50E has over other cells.
The 50E is also one of the worst performing ultra-high capacity 21700’s, along with the 48G. TBH, and with no disrespect towards those who use it, I think it’s a terrible choice for esk8 use. Other cells like the 50E2, 50E3, M50A, and 50G hold their voltage up better and give you more running time. None of them are great performers above about 10A though.
Yes, the 50E is best used at only up to about 5A-7A. At above that the high-performance 4000mAh (approx.) cells like the P42A and 40T are a better choice due to their lower internal resistance (which means less voltage sag).
We all do it but comparing capacity specs is a terrible way to choose a cell unless you are discharging at only an amp or two. The “nominal” capacity spec is typically measured at under one amp and tells you very little about how the cell will perform at higher discharge levels.