While I agree that everyone who retires early must undertake some degree of self-sufficiency, I would then say that perhaps ERE (depending on your exact self-sufficiency level) is not to be equated with being FIRE?
It is true that most who FIRE do have an innate ability to be fiscally prudent (perhaps buying used furniture on Craigslist, or knowing how to shop bargain-basement sales at department stores) - but I would guess most people would be happy just having the skills to buy what they need for the most part, and use the time savings for other ventures and interests, whereas the ERE-types are far more self-sufficient in their lifestyles.
As such, while a $7k/yr lifestyle overall may not be 5x or 10x as austere as a $35k/$70k (or whatever), it forces a higher multiple level of self-sufficiency for a variety of basic and more advanced tasks, rather than having the option of paying someone that being FIREd allows.
ERE is more about being widely skilled, resulting in some measure of self-reliance, and idealizes the Renaissance man or "competent person". It doesn't mean replace earned income with homework/steading. Making a solution is often quicker than buying a solution, so ERE doesn't take more time on a day to day basis than consumerism.
Admittedly, learning the skills (which I personally get a kick out of; it makes me happy) does take time. However, consider some random person who spends 3 hours a day watching TV. That's 1000 hours per year that could have been used to develop competency in three skills per year. Over time, the skills add up.
Of course having these productive skills also makes it possible to recognize quality when buying stuff. This results in further savings by avoiding consumer junk. It's one more opportunity to save money.
So, according to my priorities, FIRE is simply a side-effect of ERE when combining the lifestyle with a normal income. If I don't need to buy things, what can I spend the money on? Well, I could invest it and spend it on FIRE. There you go...
There are people who have multiple skills, multiple small sources of income (various jobs, investments, passive websites) , and a great deal of control over their lives as well as economic resilience but who are not FIRE (can't cover their entire expenditure with strictly financial means) because they never had a sustained economy-level (say, $30k/year) salary. I'd still tag those as being more ERE than someone who sold a dotcom company for a million bucks at age 27 and now spends her time traveling.
I suspect that MMM's budget is about as far as one can take it by making savvy choices in terms of where to live (in relation to where one spends most of one's time---usually the job), what to drive (a bicycle and occasionally a car), and where to buy things (e.g. craigslist, ebay, ...). This is about twice as efficient as the average consumer.
ERE's budget is then about as far as one can take it by adding a collection of McGyver/production skills (not that MMM doesn't have some too, he knows how to weld which I don't). This is about four times as efficient as the average consumer.
Beyond this (Pareto law), the actual time effort begins to enter. While it's possible to save money by working more (homesteading), it's not very efficient from a time-perspective. Like it's easier to buy a toaster than make one from scratch. It's still kinda interesting/fun though. What I'm saying is that there are ways of life that make some people happy (although not me, I'm not into homesteading per se) that requires even less money than ERE.
So in my opinion, peak happiness can come at all levels of income when corrected for skills, effort, and lifestyle. Just gotta read the right blogs of the level that one currently aspires to. Guess what I'm reading ;)
Also see Wheaton eco scale.