Well as I have said before this is a forum for opinions and comments and as long as it is such I will continue to share mine, pointless in your view or not! Anyway in response I would make the following comments
1) I am fully conversant with the way airlines operate their fare structures and the algorithms they use. That said I do not think it right that there can be such a variation in fares. Put it this way how would you feel if your local supermarket wanted to charge you £10 for their last loaf of bread that somebody a little earlier had paid 85p for? In my view its not morally right.
2) I have no desire to place a cap on fares rather I would expect a well known company who likes to at least create the impression of being a low cost airline to do the right thing by its customers. In effect there is some sort of cap the airline use because it stops at say £380 or whatever so if someone at Easyjet thinks that is acceptable I certainly don't especially for a once a day service to Gatwick at random times. I don't expect charity but I do expect a fair price.
3) Consider why Easyjet are flying three times a day to Jersey and their ticket prices are a fraction of those to the Isle of Man are they making no money there?
4) I do not believe that they need to run fares at £380 from London to the Isle of Man to make the route profitable. Its interesting that this has only happened recently when there is only one service a day and no alternative.
5) Its great that you have a schedule that allows you to book in advance maybe other people are less fortunate than you in this matter.
6) I would hazard a guess that the Isle of Man/ LGW route is one of Easyjets most profitable right now.
In summary my opinion is that something needs to be done to urgently improve connectivity and prices from the Isle of Man to London. Airlines, business and the Isle of Man government should be making this a priority to sort this out.