Upgrade body or lens ?

[MarceloVP_ART]

Hello, my camera is an A6000, and I have the kit lens 16-50mm and the 55-210mm zoom lens. I have started doing sports photography (specifically trail running).  
I’ve noticed that the aperture of my lenses prevents me from achieving well-exposed photos, and the focus (especially continuous focus) leaves a lot to be desired.  
My question is: should I go for a better, brighter lens, or consider upgrading the camera body (I had the A6500 in mind)? But I’m also not sure if using a higher-end camera body with my current lenses would result in any improvement.  
Any ideas, advice, or comments would be greatly appreciated.

[Cameratose]

Start with glass. Get a fast prime or two. 

[Pieter]

Fast glass doesn't help you much in getting better focus acquisition. In really dark conditions it might help a bit to get more light to the autofocus system, but with moving subjects the advantage is largely offset by a thinner 'depth of field' ('depth' of the plane perceived as sharp focus). I also think a prime is pretty challenging for sports photography, when standing on the sideline. That being said, fast glass does help to increase your shutter speed and prevent motion blur. In my opinion, an f/2.8 zoom is better suited for your use-case, such as the Tamron 17-70 f/2.8 and 70-180 f/2.8.

In my experience the AF system of the A6000 was lacking for moving subjects. By the time I had kids running around I found that the A6000 just couldn't keep up, especially when they were running towards me. This was when I decided to upgrade my camera and my keeper rate went up quite a lot.

Edited November 11 by Pieter

[Phormula]

Agree with Pieter.

Actually, you need both. A faster lens, especially at the telephoto end, will help you better isolate your subject against the background, which in action photography is almost always a bonus. It will also allow you to use faster shutter speeds without risign the ISO too much. A 2.8 zoom will help. However, if the present issue is getting a moving subject in focus, the newer bodies offer a significant improvement over the 6000.

[Cameratose]

I shoot motorsports that run from broad sunny days into night. Even with a wide open 1.8 lens and the track's LED lighting my A1 and A7 IV will push to ISO 20000 and more if I let them, something that A6000 won't do. f/2.8 under those conditions is not enough, especially with APS-C. 

I typically start with my preferred focal range lenses in good light, usually with a polarizing filter. These are either f/4 or 4.5-6.3 zooms. Once the sun is no longer glaring I remove the polarizers which gains a 1 to 1-1/2 stops. 

Then comes dusk, and it's time for the 2.8 lenses. Those will usually carry me for about an hour to an hour and half. Seems like a short period of time to warrant another pair of lenses, but it's too dark for my preferred focal lengths and not as much of a focal length compromise compared to faster primes.

Then the lights come on and it's dark. Time for primes, usually a 24/1.8 for when I'm right next to the cars and a 135/1.8 for farther away. I wish I could get a longer fast f/2 or better prime, like 200 or 250, but no one makes them. 

If you want to freeze action while keeping ISO down, the only other option is a faster lens. I have been successful shooting Karate tournaments in normal (LED) gym lighting with a 2.8 lens, but anything less than that in lighting and you need more speed. If 2.8 was enough I would've bought a 35-150 a long time ago. I could live with the f/2-2.2 from 35-60 range, but beyond that they're too slow.  

Edited November 11 by Cameratose

[Pieter]

Your use case sounds miles away from OP's so they're hardly comparable. You don't need 1/4000 sec shutter speeds for trail running. Neither will people be running in the dark. They'll likely be running during daytime in an exposed or forresty area, where a shutter speed of 1/200 - 1/400 sec should be plenty fast to freeze most of the action. An f/2.8 zoom will be totally fine in these conditions, especially for hobbyists.

[Cameratose]

45 minutes ago, Pieter said:

Your use case sounds miles away from OP's so they're hardly comparable. You don't need 1/4000 sec shutter speeds for trail running. Neither will people be running in the dark. They'll likely be running during daytime in an exposed or forresty area, where a shutter speed of 1/200 - 1/400 sec should be plenty fast to freeze most of the action. An f/2.8 zoom will be totally fine in these conditions, especially for hobbyists.

Well, no, it is in fact very similar. One of the guys I shoot with also shoots NFL for Associated Press. Another shoots High School Football (American) and Track and Field. They use the same gear for both. Fast action is fast action, and low light is low light, regardless of the subject matter. Ok, yeah, we probably don't expect someone to run 250MPH, on the other hand I can pan on a car with a slower speed shutter, while human sports requires a fast shutter to freeze leg and arm motion which is more demanding than a body moving through the frame.

I regularly get by with 1/800 or slower. If I want to show flames coming out of headers I shoot at 1/320. If I want to show motion blur I shoot at 1/80-1/160. You also have to consider that an APS-C sensor will be more challenging in those settings than FF. I have used M-4/3, APS-C, and FF. When the light gets low, there is a clear difference. 'Forresty' areas get dark, the deeper you go the darker they get.