Wowza! What a statement!
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but you do go on to say that you're not familiar with mirrorless... so I wont have a heart attack!
DSLR's (WARNING - General Sweeping Statement Alert...) aren't the best things to focus manually with and infact I'd say it's very difficult but with a mirrorless camera you're seeing a representation of the image on the chip and you can focus at a high magnification. It's like macro at a distance. With the appropriate lens and a magnified view you can focus very accurately on detail you can't even see when using a purely optical system and looking through the OVF. If anyone wants to manually focus I'd say that a mirrorless camera is probably the tool of choice
And what might the subject be doing while you are pressing various buttons and trying to see the zoomed in image on the EVF or LCD screen to fine tune the focus?
I think cameras (and interchangeable lenses) can be likened to golf clubs to a certain extent (the ones you play golf with, not the ones you join to pay golf). There are budget ones, toy ones, beginner's ones, enthusiast ones, professional ones, etc., and you can easily spend more than you need to for the standard of game you might actually play (and you can also end up buying far too many clubs, but that's another story!) However, and perhaps most importantly, there is no one, single, type of golf club that is best to use in every circumstance. You probably wouldn't do very well teeing off with a two handed putter, or putting with a sand wedge (although a world champion might achieve better results doing that than I could using the
right club - but then again, I don't play golf!).
It can be the same with cameras (and lenses); one that lends itself to be fine tuned to perfectly focus on a static subject at close range would probably not be the best choice for freezing the action of a goal strike, in perfect focus, at a football match; or capturing the spit-second moment of impact of a high-speed motorsport crash.
From the OP's description, he appears to be wanting to do different things: Capturing splashes (split-second timing to freeze fast motion), still-life shots of light reflecting off ice in water (where micro focus facility might be handy, providing the ice wasn't floating about), and capturing drops of ink diffusing in water (capturing random 3D movements of a subject at relatively close distance) are what I think was given above as some of the potential subjects being considered. If so, micro-focussing probably isn't going to work too well on diffusing ink droplets, unless the exact point of dispersion can be replicated time and time again for as long as it takes to get the desired effect? I've never done shots like that, but I'd imagine the ink in water one would require a good depth of field technique rather than micro focus on an exact point? Then there's artificial/studio lighting - best of luck there, that's an art in itself (and one I've actively managed to pretty much avoid for 30 odd years!). In addition to this, the results need to be able to be printed at a large size, which probably rules out using a 'good all-rounder' type compact camera?
It seems there's a lot to weigh up and consider, and a few different techniques will need to be researched, studied and practiced, but the 'right tools for the job' probably can't be fully chosen (or accurately suggested) until the scope of the tasks involved have been finalised. It's a bit like trying to choose just three or four golf clubs to play a round of golf with; it's possible, but I imagine knowing the type of course you're going to be playing would be important to your choice, and your chances of success.
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