Although im not sure if LAS would be a viable route for LS as TCX operate from MAN, then you have CO, US, DL, AA with one change, and also BA start there LHR service this month which i think is daily, along with VS from LGW again Daily.
My money would be on SFB initialy.
Don't quite follow your logic on this, Orlando in operated from MAN by all the charter operators, and Virgin, along with the US carriers and BA with one en-route stop. LAS is only operated by one charter operator, whilst there's less demand for LAS over Orlando I don't think your arguement stacks up at all.