Is a long run really that important?

Nope. They are extremely overrated.

Longs runs are essential

Long runs are very important. Don’t put too much emphasis on the “long” part though. More accurate would be a “Longer Run”. Aka, not just a standard distance day

The more important indicator is weekly mileage. Also Kessler is more 800/1500 than 1500/5k. Think as you aim more towards 5k the long run becomes more important.

I think it depends what you mean by 'long.' If long means 20+ miles, then no, you don't need that for shorter races. I think it's important to do long easy runs that are at least longer than your longest hard days though. For example if you do something like 5x mile at 10k pace (not a crazy workout for a 5k runner), plus 400m recovery between each rep, then a 1.5 mile warmup and cooldown, that puts you at 9 miles. If that's also the farthest you ever run, it's gonna be tough from both a volume and intensity standpoint, which is not really the goal.

Highly dependent on the distance being trained for.

Nope, it’s all about the kick. Practice sprinting everyday

No. You are clueless.

Wrong.

I think one can be very successful at 5K without long runs, especially if they are accustomed to running doubles.

One of my favorite quotes from a runner was Benji Durden talking about the importance of a long run.

Of course, he was a marathoner.

A long run for a 800/1500 runner might be 8-9 miles.

Run it within yourself, feel your kung fu as malmo says.

5k and under I don't think so. If you're in hs running an hour or 75 minutes will do 10-12 miles

Brosnan has said his athletes only do 3 a month tops. Kind of like Hobbs Kessler

yes long runs are essential during aerobic development phase.

long before super shoes, bi-carb and before doping was common the great Peter Snell, world record holder and two-time Olympic gold medallist would do 80-100 mile weeks with some 22 milers.

Incorrect. Cardiac efficiency is improved for all distances from 800m to ultramarathons by including an aerobic phase with long runs. Do the long runs. And long is not 90 minutes. Two hours bare minimum.

NONE of the top 1500 runners do this, including Jakob.

I do believe in the long run (90min-150min), but if the concern is that its too taxing, you can work around it either with doubles, or a low impact cross train like elliptical or biking.

Some do and it was proven 70 years ago practically and the the scientists confirmed it. While there have always been athletes who don’t train exactly that way, but did Jacob get out kicked twice in global 1500 championships? Yes he did.

Coe ran up to 100 miles a week in the off season. Long before super shoes and bicarb and ridiculously fast rubber tracks.

I think Kessler does too little mileage if anything. He'd probably benefit from a 8-10 mile long run, but nothing more. I heard he's longest runs are like 7 miles which is a bit too low in my opinion. I understand he has 1:43 speed but if he wants to improve his 1500/mile he needs to slightly increase the aerobic base training. 40-50 miles would be fine