The thing you have to remember is the world has changed since the days when TOM / MON / TCX bought their 757s & 767s - heck TOM were BY / AMM & TCX were JMC / Airtours / etc! Back then the low cost model was in its infancy & at many airports didn't exist at all. People booked charter holidays, tour operaters filled BIG aircraft, fuel was relatively cheap, governments weren't taxing aviation off the planet, nobody thought a great deal about the environment, or paid to take bags in the hold, the world was round & all was well.
Today, the world is still round but most of the rest of these statements no longer hold true. Even your observations about 787s being for longhaul could yet change - simply because people are being priced out of longhaul destinations. It was certainly Thomsons original plan but plans sometimes have to change.
I for one do not believe the end of package holidays is nigh however I do know that to survive the remaining players have to change. ...& one of those changes is to accept that 757s are maybe not the aircraft of the future. If they were Boeing would still be building them (or a more fuel efficient equivalent!)
Business runs to make money & running lots of small fleets of aircraft in most instances is a sure fire way to lose it. Now if that means some routes are no longer able to be offered then so be it.
Just like the dinosaurs these businesses have to adopt or die. (Oh - & hope they don't get hit by a giant meteorite! In that case: all bets are off!!)