The only reason I looked at the measurements because you said the Mavic Pro is not double the size but as we can see it is even more than that at ~2.4 times the size and over double the weight.
That is a big difference any way you look at it. If the Pro was double the size and twice as heavy as it is would you consider that a big deal? If you are saying that putting them in a case makes the difference less significant, that case has to be over double the size and will weigh a lot more than twice as much (with accessories), so I personally would call that a very significant difference. If it were a few mm's bigger and a few grams heavier, sure, but it's far more than that, to the extent that it is illegal in some countries where the Air is not due to it being under 500g. The Air even inside it's included hard case is significantly smaller than the Pro.
I have had a Mavic Pro with me before (I spent several days with one), I can tell you that none of the various carrying cases I have for my Air will fit my Pro (and definitely not with accessories). I can also tell you that none of my camera bags (I am also a photographer) will fit the Mavic Pro in it along with my camera gear, when I can easily fit the Air + accessories in alongside everything else. I can even fit the Mavic Air in my coat pocket or the water bottle mesh on a backpack if I want to - neither of which would even come close to holding the Pro. I can appreciate that the Pro is still very compact for what it is, but it requires an entirely different set of considerations for packing and/or travel.
Fair point about the batteries, but for me 3 is plenty (45min of flight, and I am never needing more time before I can charge up again). I understand that may not be the case for everyone and flight time is undoubtedly a primary advantage of the Pro (about 50% more than the Air). I also suspect 4 Air batteries still take up less space than 3 Mavic Pro batteries but I'd have to double check the dimensions.
I am not sure about the drone laws in Greece but assuming you are also not allowed to fly a drone outside visual line of sight without a spotter (who also has to be able to see the drone with a spotting scope or something similar), nobody can fly much beyond Mavic Air CE range legally unless you have a second person with binoculars or a spotting scope, which is doable but very inconvenient. If you do not require that, consider yourself lucky
Anyways, as much as I have enjoyed our friendly discussion, my only real points are these:
1) The Mavic Air VS Mavic Pro/2 size difference is rather significant at ~2.4 times the size and over 2 times the weight, and the Pro batteries, remote, and accessories are all larger and heavier on top of that. Whether that matters to you or not is entirely subjective, but the significant size difference is very much an objective one.
2) We are very lucky that a manufacturer like DJI who has a complete monopoly on the drone market makes enough drones to keep everyone happy. I think a Mavic Air would compliment a
Mavic 2 Pro perfectly, which is what I plan to add within the next few months.