Right idea wrong issue !
The european insurance requirments are a good idea for normal cases and do adress the long overdue requirement for ALL aircraft to have insurance and this has to be a good thing after all if an aircraft damages something then compensation has to be found.
However how else should the levels of liabilty be set ? MTOW sounds the best way to me.
The underlying issue in the case is tha the warbird industry is prevented from making the money it needs to fly such aircraft because they are not allowed to charge for joyrides or trainning because there aircraft dont have a public transport C of A.
Remove this restriction and the industry could stand on its own feet and the cowboys who sell you a £300 teeshirt and give you a free ride in an old aircraft will be driven from business by CAA inspection.