It’s called premium economy and it exists on most major airlines.

Not on Southwest, which I generally prefer for other reasons, but United almost always has seats with about 6" of extra leg room available to upgrade to for 10%-20% more, as an option. I often pay for this. For the comfort itself and to support such an option. I just don't like the fact that the easy thing to sort over on flight search engines is price and airlines like United now often have the cheapest seats the middle ones.

Shop around airlines, you can find some that offer a middle ground - Premium Economy or Exit Row.

At 6'2" I've never really had a problem with someone reclining in front of me, and if someone behind asked nicely I'd go to upright lock position.

Of course, I usually don't have a foot bag which makes a big difference.

Probably because the profit they'd lose by business class travelers downgrading to it would be more than the profit they'd gain by economy class travelers upgrading to it.

There is: premium economy.

Also, business/first class is often much less than 5-6x the economy price. In fact I'm not sure I've ever seen it that much higher.

Business class is just that - usually paid with someone else’s money and therefore those passengers aren’t price sensitive.