Name it and i probably have tried it, or at least pursued with a modest intent and funded by my own wallet.
Leica M9, 4/3 systems, Sony A7R, Xvario, MF film cameras like Texas Leica, M6 titanium and the list goes on.
When i got my Sony A7R, i thought this is it, a camera that allows me to use any lens and whose manual focusing draw circles around the M9.
Few months down the road and after i have done various projects and albums, i am back to the DSLR and never been happier. Instead of trying to be a contrarian and troll around the blogs, i gonna just list out 7 reasons why i switched back to DSLR by listing out the counter behind some of the current points for mirrorless, particularly for my type of shooting, outdoor portraiture.
Here is the catch though, i do believe that mirrorless is the future, just that the future is not now.

1. Mirrorless is lighter and smaller
Yes it is. But its not that small that you can put into a pocket. In malaysia or tropical countries, its pretty hot, you don’t go wearing a big jacket with big pockets. If any, you be wearing jeans or shorts. Regardless of which system i took, m43 or sony a7r i ended up using the same bag. For short trips or outdoor, i even carry less batteries on the dslr simply because it lasts so much more, the currrent nikon DF i have could go over 1000 shots. Cant say the same for any of my mirrorless, heck i even end up carrying the charger “just in case”.

2. APS-C vs FF is negligible or m43 is sufficient
Yes and no. Smaller crop cameras comes with expensive shallow depth of view to boot. m43 for example, 25 mm 1.4? ouch, thats just 50 2.8 in FF terms, when it comes to how shallow it is. The cheapest 50 1.8 in FF would cost a bomb in m43. What about APSC vs FF, surely that is sufficient. I one read about this Zack Arias that APSC vs FF is negligible, while i agree of the point of sufficiency in image quality, i can’t agree when it comes to how expensive or hard it is to get equivalent focal length in APSC.
The nikon 58mm in FF is 87mm in DX (APSC nikon). 58 mm -> 87 mm, OUCH, there is nothing negligible about it.
So if your birding, oh yeah..that would work.

3. Sony A7 is FF and mirrorless and supports tons of legacy lens.
Yes it done, mostly via manual focusing or some strange adapter. On legacy lens, while the bokeh and rendering are interesing, the image quality of anything other than centre is often inferior, significantly, some exceptional lenses like Leica and a good novoflex adapter would be the exception. While doing manual focusing is fun, it totally limits your creativity in getting candid and natural shots of people.
Did i mention the battery life is a downer? If you think about it, why is it until now, there are still no fast autofocus aperture lenses like 1.4 for the FE mount?
U can wait for that, i love the 1.4 bokeh and object separation it provides for portraits. Heck its the magical aperture that gives bigger sensors like MF a run for its money.

4. Build quality
Sony probably didn’t think too much about people using strange lens on its mount. The thin mount on the sony prompted third party to release a mount replacement. Its not a very enjoyable shooting experience knowing that some nice lens you have would actually kinda make your whole camera flimsy. Leica M9’s cracked sensor, failing led indicators and fading wordings shows that price is not exactly quality either.

5. RAW files
Lets face it, adobe PS an LR is the gold standard. I don’t want to tweak around with other apps to get better result, filters and effect, yeah maybe. Its kinda ironic that this has nothing to do with mirrorless vs DSLR, but its just that the file format and strange sensors (x-trans) introduced by some brands on their mirrorless is touchy.
I actually like Leica’s DNG format, its from adobe anyway and fully supported. Olympus, Fuji, Sony …well, there is always this voice at the back of the mind that whatever is on my workflow is not good enough.

6. Flash, tethering, lens correction …
A host of stuffs we took for granted in using DSLRs…are wishlists in mirrorless.

7. Lens quality and Autofocusing
While i could not say for sure if canikon produces the best lenses in town, but it does seems that they give good value for quality and autofocusing CORRECTLY is the norm. There is a big difference between a fast autofocus and an accurate autofocus. There is a huge support for lens for DSLRs while every mirrorless wants to have its own mount and inconsistent pricing and lens quality.
Wide angle on a mirroless is always a bit lacking in choices, Sony A7(whatever). It seems that lenses made for leica rangefinders like 15mm and 18mm just don’t produce the same results here too, although i personally use the 18mm CZ and 15mm VG for portraiture, i know many landscape shooters that struggles to get a proper set of wides.
Using legacy lens means u have no exif data. Cataloging is a pain. Its near impossible to capture natural and candid like shots of portraits when you are doing manual focusing on the mirrorless.