Flex still requires an organised group to start with, and still someone in charge who can set requirements potentially excluding someone who knowingly cannot commit to a full raid.
That is why LFR is still necessary, the very reasons why LFR exists in the first place.
Your spot in Flex is still dependant on the willingness of others, which given the absolute need for the LFR format is simply not as forthcoming as it should be.
Flex still ensures the possibility of "Full raid or GTFO".
The community forced the need for LFR, and the continued poor attitudes of those bashing LFR ensure its continued inclusion in the game.
Ironic that those complaining most about a feature are the very reason it exists.