Yes, Harriers can be difficult to shoot due to their maneuverability, especially in windy conditions. I tend to use the 180-600 for Harriers and Ospreys or anything where the range can change quickly or can be erratic. That said, I finally caved and picked up a 600TC today for long range work with TC's, but am curious to see how well it works in similar conditions by toggling the built-in TC. I know by experience that fixed primes are an exercise in frustration in these situations.
Anyway, you had some nice closeups and did quite well IMO. Not often we can get that close to them around here.
I don't mean to detract from your post but if you don't mind and FWIW I recently posted this on my YT site using the 180-600+1.4xTC in 4k120p 2.4x crop mode where I also have a few of NH videos. If the quality isn't great, it's almost always due to atmospheric conditions...