I agree Anthony, and here’s my point. Governments (especially, but not limited to, the EU) impose so many regulations to keep us safe and healthy from rules regarding conkers, food to safety features in cars that I’m surprised they have not yet legislated in this regard, especially as there are more and more cases involving DVT after airline travel. Precisely because it rarely hits you during travel, so you’re not dying on the plane, that it gets much less publicity than it deserves.
I’ve not experienced PE other than a mock up Lufthansa had at Malpensa airport whilst promoting it just after its introduction, and it reminded me of long haul travel in Economy in the 70’s and early 80’s. Quite comfortable and more than enough legroom for someone just over 6’1″.
As for airline advice to move around during flight, if just 10% of the pax did this there would be chaos and pandemonium, especially so in single aisle aircraft, and if done over US airspace would probably get the plane diverted and them arrested, so it really is not practical advice and one the airline would probably react in horror to if everyone actually followed their advice