Whether it is even a problem to be solved remains a matter of opinion.
I would say it's definitely a problem that the meat of this game for long term players (BGS) is easily 'gamed', and the gamed faction can't do anything about it if the perpetrators are in solo.
How big a problem is definitely up for some debate. Should something be done to make it fairer? CAN something be done? I dunno, but to pretend that it's all good and working perfectly, is as as just as unrealistic as suggesting that the 'BGS should not be affected by actions in solo'.
I don't know what I'd do, but I wanted to point out that just because any potential change would not affect the cross platform problem, that wouldn't be a very good reason to therefore do nothing or ever try to make it 'fairer'.