I found Shadow's game fun, and he was already fairly dark/dank/etc. Even his own theme song in SA2 made it clear he was meant to be like that. Him suddenly swearing is where it goes all haywire. The guns don't even seem that odd, as he grew up on what is literally a military base. Though yeah, the stories were disjointed pretty badly.
For the most part, the guns make sense, but he shouldn't need help to deal damage to the humans at least. The mechs and Black Arms, sure. It was already established that large mechs take multiple hits in Heroes anyway. Black Arms are the same race as Shadow and literally could be of a similar toughness, so they are harder for him to kill. It's also possible he's not at full power yet, since he was overall brought back after using all his power in SA2. He wasn't that strong in Heroes either, no more than Sonic, Amy, or Espio. Chaos powers, sure, but that was it. His new Chaos power wasn't even usable till you got a Chaos Emerald properly(you can actually do so, but the Emerald is meant to signify when it's "officially available" for story purposes). Which does make sense, as Chaos Control was an ability he always had an Emerald with to use. Chaos Blast makes sense too, the dark variant of it.
The cheesy lines were honestly fairly bad, though fun. I'll still take them over Heroes, which was too cheesy. Some of these felt better written overall. That said, Shadow's game also had a lot of great music, including remixes. I wish some of it was in Smash.