SimsP

Well part of all of this is true and part of it isn't.
In the beginning everyone should answer one simple question: What do I want to get?
Do I want to use the footage just the way it comes out of the camera and put it on youtube? No grading or colorcorrection. Well why buying a GH5? Save the money and get a cheap DSLM or maybe even your smartphone will do the job.
If my demand for quality is a little higher and  I want to grade my video a little bit, but I don't need my camera for paid jobs maybe a a6500 is a good choice. For paid jobs a GH5 is probably a better choice as it is a little more versatile. And that's it basically. For youtube or even television you really don't need better cameras.
But things start to change when it comes to high quality Hollywood class video, especially concerning the recent approach of HDR for video. I've been playing with the new possibilities that you have with this huge dynamic range for almost half a year now and the one thing I have learned really quickly is: NEVER USE 8 BIT!! Although for SDR video with roughly 6.5 stops dynamic range 8 bit quantization still creates pretty decent quality, for HDR it is a huge pain and limits your grading possibilities drastically, especially when combined with an end-user codec like avc or hevc. That's why recently I've been starting to use an external recorder for my NX1 which doesn't help me with the 8 bit problem, but recording Prores helps preventing lots of blocking artifacts. Actually the 10bit output is right now the one thing I envy all the Panasonic GH4/GH5 owners for.
So what kind of cameras are well suited for HDR video. Well first of course your sensor has to have a high dynamic range and this is where expensive cameras are still almost undefeated but also the cheaper cameras like A7s have a great sensor concerning dynamic range. GH5, NX1 and so on deliver quite decent dynamic range, but actually you can tell the difference to more expensive sensors in post.
The next important thing is quantization and this is where all the cheaper Sony cameras as well as NX1 and Canon cameras really suck. 8 bit is definitely not enough for HDR and you will get a whole lot of banding if you're not very careful. In post I very often use a grain overlay on my NX1 footage to dither the banding a little bit and it helps, but it's far from perfect. So when considering HDR 10bit recording is absolutly minimum. Better use 12bit or 14bit if possible.
The final really important thing is the way you store the data. Here the Blackmagic cameras clearly have a huge advantage because of their RAW capabilities and my BMMCC has served me very well during the last couple of months. Using RAW you can make the most out of the sensors dynamic range. Prores or DnxHR also do a quite good job but you will most of the time lose at least half a stop and this is something you definitely do not want for producing HDR content. So whenever you can afford the datasize SHOOT RAW and NEVER EVER use AVC or HEVC they will betray you.
Actually this leaves not many cheap cameras in the pool. The only cheaper cams for RAW are the Blackmagic ones and the next would be FS7 price tag and beyond ARRI/RED.
If I had to choose a camera for a professional grade HDR production never mind whether for youtube, TV or cinema, the cheapest A cam I would go with would be a Blackmagic 4.6K and maybe a BMPCC/BMMC or perhaps GH5 as B or action cam. Every other camera below has too many limitations in one way or another and obtaining good HDR footage will be very frustrating.
But the price is worth the effort. HDR with its huge dynamic range allows for a whole lot more creativity, when it comes to playing with lights, shadows and colours. In my opinion HDR is the one big thing during the next years, that will allow us to be even more creative in pictorial design than ever before and hopfully it won't follow 3D down the stream.

So, as mentioned before, the question always is: What do you want to get? For common youtube quality you don't need a camera for 1k+ bucks. But if video quality is substantial to you, especially when you're considering HDR video, the range of small affordable cameras becomes smaller and smaller. Thus if you don't want to buy a new camera every other year - choose wisely. And maybe Blackmagic has something new for us in their pipeline for the not so distant future. Kudos to them for democratizing video world like never before!