How can they serve two masters at the same time?
In the same way that people who work at Red Hat who also contribute to the Linux Kernel. Or how TOR is partially funded by the US government and had DoD employees working on it.
Not the same, no one should have any issue with the core developers developing segwig or lightning network or anything else they wish. The issue is that they have the power to decide or directly influence if it is part of bitcoin or not.
And then there is calling other solution foolish:
upgrading the Block size to pave the way for SegWit & LN". is a foolish way to increase capacity.
So by your logic Satoshi's concept of halving every 4 years is
foolish or the number 21 million is
foolish.
Function good/ Constant bad.