It's a one line team because the team doesn't have a 2C., even if Mantha and AA were healthy it's still a one line team. Flip's not a 2C and Nielsen is a joke. AA has been miserable this year, so the only other option is to try Fabbri at 2C.
This team supposedly has a lot of centers but other than Larkin, they're all 4C or marginal 3C at best. Helm, Abby, LGD, Nielsen, Ehn, Flip... not a single guy that can drive offense.
The only 2C available in UFA this season is RNH, and I'm sure he's gonna have a high asking price. (Backstrom was resigned to $9.2M, which is way more than I expected.)
RNH still has a year left before free agency. The most interesting center right now might be Pageau from Ottawa. Or if you really want to roll the dice, Galchenyuk could be an interesting grab.
Depending on how Veleno and Rasmussen are viewed, and how this draft goes, 2C might not be a long term issue, so I'm not sure how much you really want to invest in it. I'd still try AA back in that center spot. Yeah, he's been lousy this year but he didn't look bad at it last year. He's earned a look there, imo. And if he takes the opportunity and runs with it, good for us.