A few concerns come to mind:

Single player missions allow players to learn the mechanics of the game, practice the basic moving/shooting skillsets, learn their weapons/tools, etc (specific to that game) before entering multiplayer mode. This is esp true when they are being dumped into fighting matches against lvl 40+ players right from the get go (which is what you now see in Titanfall).

In addition, experienced players do not want complete noobs on their team anymore than noobs want to be killed off so easily by those already familiar with the game mechanics. This is a trial by fire method that leaves many people to drop the game early on and wonder what all the hype was really about.

Charging $59 for the game, but providing not much storyline or content in the form of single player missions, definitely places the rewards in the developer's hands, not the customer. They chose the shortcut route, yet how many people that bought the game knew it did not come with a single player mode?

We have had pure online/multiplayer FPS games out there for years (Planetside is just one example). Why not be clear in your marketing that is what you are offering? Few would bother with the physical DVD purchase then.