Powering 10 m of WS2812B RGBs
The chip uses internal regulators so all you need is 3.5V Min at the end. If you get this it works for 5m but not 10m. Thus you can distribute AWG16 or suitable wire to either 2 starts or 1 start 1 end or all 3 Nodes.
Testing the end supply voltage with 1 Start will tell you when all RGB are on what your drop is on both V+ and rise on Gnd which may be equal.
If you can get more than 250mW or more on each chip it may burn your finger but still work.  But all you need is 3.5V not 5V.  More voltage just makes it hotter. So supply enough and no more for expected performance with least temperature rise.
Thus 1 feed at each end as you have shown may be ideal. If middle is say ~4V.  But if all 3 nodes are 5V and middle of 5m is say 4.5V then your are just adding heat and not brightness.