They likely want to used pulsed lasers assuming average power output stayed the same, but physics is a bitch. So, they don’t get to arbitrarily chose.
Ok, but if we're including things which are currently impossible then I'd assume they'd rather just use Professor X and have him mind blast the missiles out of the atmosphere.
Every new design is building something that does not exist.
We already have pulsed lasers with average power output in the kw range over several hours. Even better, this thing does not need to fire for hours at a time so you can skimp on heat dissipation. But, you can buy 2kw laser cutters off the shelf.
Really, scaling it up in a lab is one thing, but getting everything else to work like dealing with vibration, portability, and targeting is hard. So, while this design had slightly better tradeoffs, that does not say much about the design space they where working with or what they consider useful vs required. Ex: What frequency is this?