Last EOS body I bought was a 2015 EOS 5Ds R
... maybe a near decade's gap would be well worth finally transitioning to Canon's mirrorless.
As a hobbyist you have to ask yourself what you are missing out? Law of of diminishing returns
I personally think it depends on how you treat the hobby.
Even as a hobbyist, having the right tool to make life easier and more enjoyable is a huge return on your investment.
Here’s an example, you could paint or woodwork as a hobby. You can buy decent brushes and tools, but sometimes having a really good premier brush, or that high end special saw and blade that will cut perfection, can make the hobbyist enjoy their hobby that much more.
It’s all up to the hobbyist to determine if he wants to spend the money on his hobby or not.
Now in terms of mirrorless, it has huge benefits over a mirror in my opinion.
If you shoot landscapes or static objects, then you might not care about mirrorless.
If you shoot humans or animals or anything fast paced, then the eye tracking and hit rate on mirrorless is amazing.
If you shoot your anything fast paced like your child’s sport game, then mirrorless has the ability to loose the mechanical shutter and shoot 20+ fps with the formentioned AF hit rate.
If you are a new hobbyist and learning photography, mirrorless offers live exposure view. You can visually see what the changes you make to the exposure triangle do in real time, rather than trial and error on a flipped mirror.
The mirrorless RF budget glass (although limited) far outshines any EF cheap glass you can buy as a hobbyist.
The RF 85 2.0 macro is sharper with better contrast than the EF 85 1.2 and 1.4 L’s at a fraction of the price.
The RF 50mm 1.8 is surprisingly sharp and beats the used EF 50’s you can buy at that price range.
If you like to shoot any type of video, mirrorless is the way to go.
It’s all relative to the hobbyist, some invest more money into their hobby than others and considering diminishing returns is relative to the hobbyist.
It might not seem worth it to you, but it will to someone else.
If you have been happy with your 5DsR for the past 10 years, then really there is no reason to upgrade and you will be happy with it for another 10 to go.
If you wish you had certain tools to make your hobby more satisfactory and enjoyable, then maybe you should upgrade to mirrorless. It’s all up to the user to decide.