What is this extraordinary belief that the building of aircraft by competing Companies in different countries should be fair?
If Boeing's influence on its country's government is sufficient to ensure that said government makes it easier for Boeing to design/develop product, then the solution that Airbus has to persue must recognise that this is happening and act accordingly.
If that behaviour causes, or threatens to cause, 'subsidy escalation' as each tries to outdo the other, then the opportunity exists to rein that in, under the direct influence of the market, as each of the governments and companies recognise that their subsidy gearing is becoming, or will become, less and less favorable (i.e. smaller and smaller benefit from larger and larger subsidy).
So economics drive the change: not a strange view that "it isn't fair".
A smart view of economics says that the subsidy race/spin/obfustication need not lead to collapse of either producer in order to demonstrate the fallacy of over subsidising - and that is the basis upon which discussions to resolve the difficulties must be held. But going into such discussions you do your credibility no good by claiming that the current position isn't fair - fairness doesn't figure in the economics unless it can produce a measurable benefit for all the major players.