Front kicks to the knee have been around for decades. It's an old move that isn't that bad as it looks. Plus there are ways to avoid it. Rashad parried most of Jones' kicks so that it had no effect, so Jones went upstairs with the elbows. In all the years of people using that kick in muay thai not many people have been seriously injured with it. Sure you can make the argument that they could get injured, but you can say the same thing about plenty of other legal moves.
Spiking heads and strikes to the back of the head are more dangerous because of the potential of concussions. Front kicks to the knee is just the same as low kicks. The thing with a lot of MMA fighters is that they have to learn to evolve their striking game past throwing punches and calling it boxing. Too many guys just stand in front of the other guy head hunting instead of setting things up. There's a way to keep those kicks from having an impact. Fighters just have to learn how to defend those kicks.
It was different against Evans, Jones didn't throw as many of them as he did against the likes of Vitor & Rampage in particular simply because Rashad is far more of a takedown threat than those guys. I'm sure Jones would have known Rashad would be training on trying to catch those sort of kicks.
However getting back to your other points, just because there are ways to partially avoid something doesn't make it any less dangerous if it lands. I mean strikes to the back of the head can be avoided if you don't turn your back to your opponent & 12 to 6 elbows can be blocked as easy as regular elbows & punches can.. heck foot stomps can be blocked just get your ass off the canvas real fast.
Don't misunderstand what I'm saying, I understand that what I'm saying is kind of ironic given that we are talking about a sport in which you can have your head kicked off & I also understand that such a strike is a legitimate martial art technique.. however so are throat/neck strikes in some disciplines.
My perspective is that if it's something that looks like it could cause a career ending injury or harm a persons long term mobility, it should be illegal. Head spikes aren't illegal because of concussion risk, they are illegal because of the high risk of breaking someones neck if you dump them down in an awkward position. Strikes to the back of the head are probably concussion related, however you can get a concussion from being knocked out or hit anywhere on your head.
Also front kicks to the knee aren't remotely similar to side leg kicks ie shin to thigh/calf. Front kicks to the knee are designed to hyperextend a persons knee, which can cause all sorts of crazy damage & I'd imagine when you've professional guys that know how to throw it correctly it will take surgery to fully heal up if they do hyperextend someones knee. There would be 6 months+ on the shelf.
Side leg kicks are essentially designed to give the person a wicked dead leg & hamper their movement, however in 99.9% of cases the damage done by these is over after maybe a day or 2 at most.. maybe a week if Jose Aldo or Pat Barry is kicking you. Whereas the front kick to knee.. well if the thing lands correctly, then you've hyperextended someones knee & there is almost certainly ligament damage done instantly. You are then talking weeks maybe months depending on how severe it is.
Rules for MMA differ from state to state, country to country, promotion to promotion, however I was just glancing at the UFC's own rules & one in particular kinda falls under the category I'd file front kicks to the knee under:
Engaging in any unsportsmanlike conduct that causes injury to an opponent
Also the California Athletic State Athletic Commisson employ these rules:
Any unsportsmanlike trick or action that causes any injury to an opponent or referee.
Linear kicks to the front or side of the knees.
no one better get injured
