What you're saying. The only reason to take a plane vs taking a train for this distance is the price. Usually planes are way cheaper. But the hassle of taking a plane is really making it a tough sell as you say.
Train tickets are anywhere between 60 and 300 pounds for this route. The cheapest plane tickets for the same route I've found were 80 pounds and there is no upper limit. I don't see much difference in price to be honest (+ getting to the airport is usually way more expensive).
I did a quick search for both April and June, and found the prices very similar. EasyJet is cheaper when buying well in advance, but it's not a massive difference.
Of course, budget airlines will also take you all over Europe for low prices. But for the narrow case of just London-Paris, the Eurostar is competitive, which is quite a bit cheaper than I'd remembered.