For me ERE frees you from the need to worry about conformity. Maybe you need to worry about conformity for the 5 years you are working, but that's a pretty short amount of time, during which time I can put up with working consecutively and shaving or whatever. Semi-ere frees me even more because now I don't need to work 5 years (which for a lot of us is more like 10-15 years) consecutively. Once I have fuck you money I can stop worrying as much because if I get fired I'll be able to wait until I find something else. Not worrying about conformity also leads to less conformity, because, as others have pointed out, sometimes the constraints are in your head and your employer doesn't actually require them. This would also be true if you could easily switch modes of employment or employers in the standard ERE plan.
Barriers to entry is different. You can't overcome these with FU money. However, I think you can overcome this with a renaissance mindset and a bit of freedom. If I NEED to be an astronaut or tenured university professor then I'm screwed (out of retiring in 5 years). But why do I want to do those things? I bet most astronauts and professors don't actually like all of the tasks required for their jobs. What aspect of the job do you actually like? You can become very educated about a specific field without being a leading researcher in it. If you NEED to be something that takes 25 years to really become, you can still do it. Saving some money and living frugally isn't going to stop you. You will still need to play the game and overcome barriers to entry, but you would have to do that anyway.
Even something like doctor is still achievable. Becoming a doctor sucks from an ERE perspective because it's expensive and time consuming. If you really NEED to do it though, it's still less than a decade of your life. I think it'd be totally achievable to become a doctor, work for 8 years, pay off your debt and reach FI. 16 years is a long time, but this is something you really really super wanted to do. I don't think most people want to go through the schooling without the payoff of a long career as a highly paid doctor, but if that's true, did you really want to be a doctor?
What I'm saying is, this difference in mindset is huge for this discussion. If you ARE the thing you do, which can only be one thing that you MUST do, then you are going to have to worry a lot about both conformity and barriers to entry. If you can do multiple things, none of which you must do, and which you select with some thought towards both conformity required and barriers to entry, then you can worry a lot less about employability.