Just now I ended up soloing Federation Blockade because the other four abandoned it before it even began. Now, just thinking selfishly, I would think I could and should get extra fleet marks just for the fact that I soloed it (and, by the way, saved 11 of 24 freighters without getting destroyed once). Unlike the Borg PvE's, the Fleet PvE's have the opportunity to ramp the Fleet Marks based on how many are actually involved in the fight.
More important than that, however, is what about people who prefer to solo and do missions? Why not solo Fleet PvE's or the ability to do a current Fleet PvE solo (obviously which makes for increased difficulty even if ramped down) as an option for earning fleet marks?