Mileage counts more than I realised

6-8 months is a long time to be injured. Should be zero.

Intervals would have made a massive difference. Without that you're basically not even training.

Gradually increase your miles. Add some speedwork.

Miles gives you endurance, speedwork gives you speed.

Once a week go to a track and do 8 x 800m, all you need, don't hurt yourself.

But also:

You mean, you previously didn't realise that doing something more would make you better at it?

Having come from mainly anaerobic sports it took me awhile to accept this, but distance running is mainly about grinding out as many miles as you can without getting hurt or sick.

Mileage works. I was doing half marathons on 40 mpw. Then I ramped up to 60 mpw to try the marathon.
So I did a half as a warmup race and dropped 3:30 off my PR just like that. Also did the fastest 10k is several years.

+1

The 5k is almost purely Vo2max. The fastest i’ve ever gotten off of pure easy to moderate running mileage was 16:50ish, and i’ve broken 15:00. It isn’t fun but if you wanna run your best at 5k, especially as you start getting faster you gotta do 800s till ya puke at one point, mile repeats until ya puke at one point, and 400m repeats until ya puke at one point in your training block or you aren’t training for 5k. When you are out of shape running a 5k, your problem is usually that your muscles are too weak to carry your body over the distance, and your lactate threshold is so low that your legs burn by the time you’re done walking up the stairs. When you are in shape, your limiting factor in the 5k is how much oxygen your body can take in and utilize, and how efficient your body can be at running fast. You get some but not much of that from running 6:30-8:30 miles, you get a lot more of that from pushing your body up to its maximum heart rate and breathing as hard as you can over the span of 2-6 minutes a few times over while running as fast as or faster than you’d want to run in a 5k.

"distance running is mainly about grinding out as many miles as you can without getting hurt or sick."

sounds like fun

You just do your low mileage the wrong way. Simple as that. 🇸🇪🧙‍♂️🇸🇪