I think Southend is going to always be a leisure airport with mainly seasonal summer sun, winter ski and popular city break destinations serving the local area of Essex, Suffolk, Kent and East London.
It's getting increasingly difficult to distinguish between business and leisure travellers these days, but if suits are anything to go by there seem to be plenty of them passing through SEN's terminals on the Irish flights.
I assume most of the people in suits are on the Aer Lingus service to Dublin, where there are onward connections to the US? Remember also that suits is not solely related to business travel. People could be travelling for all sorts of formal occasions.
Just a little background knowlege for those less aware, there are three main types of tourism. Business, Leisure and VFR (Visiting Friends and Relatives). There are other types like "Special Interest" and "Dark" tourism (memorials/things relating to death, eg. visiting Auswitch in Poland.) but these do tie into the three main types stated above.
As much as it may be hard to distinguish the different types which I do agree with to an extent, the airlines, like any business have to sterotype to what the typical type of tourist/traveller requires so easyJet's decisions will be based around this.
A 13:30 departure to Edinburgh from an airport 40 miles east of London is clearly not aimed at business travel. Primarliy, business travellers are going to choose the more conveniant Gatwick, Luton and Stansted airports for such services where the surface transport to the airport and range of facilities in the airport are generally more of a consideration than the cost. Again, seems stereotypical but that is the business world.
BFS with only one flight a day is also less feasible to a typical business traveller as they generally require a good choice of flights due to them having less flexability in flying times, days of the week etc. but usually need morning outbound services and evening inbound ones.
With other short routes like Jersey and Newquay, unique to Southend in the London area with EasyJet, I think further shows the emphasis on leisure travel, especially since the Newquay route replaced 1 or 2 Amsterdam and Belfast services.