I dare to question your statement as well. Please educate me in what specific way you think I'm negatively effected. Really curious now!
Just take the latest addition (and already mentioned) Fleet Carries. They were initially designed for Squadrons, which would have been consistent with game world, but MP-only content just as Multi Crew. Basically waste of dev time for all solo players. FCs could have been more specifically taylored (s. old design descriptions) for Squadrons. Compare that to what we have now, started from cluttered system maps, to running costs and overall expenses.
Besides that, do I really have to point out how strange it is for an MMO to have missions, that can be done by more than one player, only years after release and only with very limited variety. While at the same time having to coherent set of missions, not even for ranking up a military career. Which, by the way, is still meaningless to game, besides unlocking some ships. Bottom line is, we neither have good MP missions, nor good SP missions.
And if Fdev does create MP-only content, like the Thargoid "assault" (until Scouts were introduced), they needed to make sure it does not make too much of an impact. Because Solo CMDRs had a far harder life against Interceptors as multiple CMDRs at once. It is a compromise affecting both single and multplayer.