I would take a 12" macbook over an iPad pro any day... for a similar price,size and a proper OS.
The problem with the iPad continues to be the drawback of the IOS. No storage options and unless you have constant data or wifi then using it is difficult. The main pros are the touch screen and pen interface but getting images on and off are still a problem espeically when your not in your home environment.
I took an iPad mini 2 traveling half way across the world instead of my macbook airto save weight. It caused all sorts of issues with expensive work arounds. This was 2014 so things were not quite where they are now.
I was using my 5DMKIII, shot raw to one card and small jpg to another to send to the ipad. I had to buy a hyperdrive to back up my images as I shot around 3tbs in the 6 months I was away. This also gave me no redundancy and there is no way unless you buy two and at the time they were £400 each. Then you had to carry lots of dongles for the ipad too. I had lots of issues with the ipad, but most of those have been solved. It was a Gen II so the colour accuracy was non existent looked great on screen then lots of people gave me feedback about how saturated the images were.
The ipad was a 128gb and after the 6 months of selective image importing and editing it was full... Small jpgs... just not ideal.
I traveled Rio to Lima in South America and the wifi was poor across the board. Using a back up service was out of the question and something like lightroom sync wasn't possible either at the time but the wifi strength wouldnt have made this possible. I then traveled the US and again I was on the road a lot traveling the national parks so signal was poor and slow, in most of the hotels WIFI was not included and you had to pay for it... so weird as pretty much everywhere in the world it was free... anyway same problems.
The second 6 month trip a few weeks later I took my 11" Macbook Air i7 512 ssd and it was bliss, took 3 hard drives one 1tb ssd for edits and 2 4tbs. Kept the drives in separate places for redundancy. The nice thing is you have access to a full OS with a full suite and you can edit proper files instead of what I was doing on the ipad, editing a small jpg with no metadata then having to replicate it for a full resolution version when I got back, really time inefficient. I traveled 3 months across Africa in an overland truck around 25000 miles with this combo and it was brilliant, no worries about backing up etc I then did a 3 month stint across South East Asia.
Obviously my situation is different as I had a purpose it wasn't just an additional tool, I needed a fully functional travel companion. Until Apple gives more flexibility where these products dont rely on wifi and 4g then they are very difficult to use unless you are close to home or have one shoot and offload. Another problem is the size of it unless your at a table balancing that thing is difficult... let alone doing critical work... if your on a table use a proper machine...
The other issue is the 12" macbook is a similar weight and almost the same price...
My 11" MBA was stolen
so I replaced it with the absolute base line 2015 1.1ghz macbook with 8gbs ram and 256gb ssd (because at the time money was an issue). It turbo boosts and it runs everything adequately and has the retina screen and excellent battery life and is about as perfect to a travel companion as it gets apart from its one port which makes attaching storage and a card reader difficult as it cant power them both at the same time... Huge over site. It will edit 4k footage in final cut no problem either its really quite impressive.
The newer 2017 versions have much more power with the M5 and M7 chips but still lack twin ports. The base MBP doesnt offer a lot more but one extra port and slightly more powerful and probably less thermal throttling.
I run a mac pro as a desktop solution and when im away its so nice to start a new lightroom catalog import my presets and edit images on the road then import it back into my library when I get back with the edits already done. If you work this way, which most pros do then having a super powerful portable isnt really needed.
When your using 30-50mb raw files cloud sync just isnt a good option eats data and takes forever.
Things are getting there the ipad just needs a port for external storage to be worth anything to a professional until then its an expensive novelty purchase.
Currently a dedicated machine is still king IMO.