I believe that is incorrect. You can use those weapons solo. Just the reloading is going to take longer. We'll see soon enough.
In the original game, strategems like the rocket launcher and other heavy weapons had long reloading animations to avoid spamming heavy ordinance and keep the difficulty in check. So you had to pick your spots when you wanted to reload heavy's, and if you misstimed, you would get overrun in the middle of the animation and either die, or cancel the animation and flee, at which point you had to start all over again. That was good at creating tension but for noobies and casuals it was also a source of grief.
By adding the teamwork component for faster reload, not only do you incentivize teamwork, you lessen the potential grief.