I wouldn't worry too much about that to be honest. They needed to spend a lot at launch as they were effectively launching the sector for 'All Biz Class' flights, not just Maxjet as a brand. The marketing will probably also include PR, launch events etc too, hence the higher cost.

Yes they have more routes to support now which would need more support at the US end, (i.e. ex LAS, ex IAD etc) but not at the UK end.

3 million is actually a very reasonable marketing budget for an airline of their size.