Maybe, the middling 70 was chosen for spirits since full bottles aren't drunk at one sitting.
Sort of - it's because standard measures in the ontrade are either 25ml or 35ml and they both divide evenly into 70cl (assuming you pour accurately) so that's what the EU defined as the standard for spirits in 1990.
You might also want to learn the difference between the US liquid pint of 473ml, the US dry pint of 551ml and the (British) imperial pint of 568ml...
It's all performative nonsense this pint bottle thing - the sizes of smallpack containers is dictated by the huge economies of scale of the big boys, you can pack beer in any size you like but there's no real "choice" - cans are almost all 330ml and 440ml cans (and very rarely 568ml) whilst bottles are all 330ml and 500ml. About the only exceptions I can remember are Heineken trying to rip people off in sports stadiums with a 400ml and the occasional 650/660ml bottle.
Even in the US they've taken to using 19.2 US floz cans as their "big" size - because that's an imperial pint, and they can get the cans from the UK rather than making a new size that makes sense in USian.
So I can see the odd pint bottle being made here just to make the point about Brexit "freedom" but the reality is that it's going to cost about the same as 75cl thanks to the lack of economy of scale so it's pointless. You can't buck the market....
If they were to make any changes to drink sizes that would actually mean something, it would be to allow draught beer to be sold in 1 litre amounts so that we could import fest glasses from Germany rather than needing special 2-pint ones that cost a lot more.
And also do something to legalise a small amount like 4 floz or 100ml for "pay up front" beer festivals which are currently illegal under the letter of the law but which generally have a blind eye turned.