No problem with a seagull striker. Absolutely no issue at all and I can't understand the issues with it.
It rewards a fantastic run by Boxall. If Boxall has made that run, Burns could have made that run from an onside position. Also the defenders could have made the run back to cover him. They still can't pass to him in an offside position- the winger/forward/fullback has to make the run from an onside position past the seagull striker and play him onside. If the defenders are actually playing so well they'll get back and cover him.
Don't think the argument against it stands.
If you rule it out there are all sorts of minor issues in the box that will be really difficult to ref.