When your bill for that same or similar type meal in a Disney restaurant is to the tune of $180, leaving $40 makes it a very expensive evening out, particularly if you are dining this way every day for 2 or 3 weeks. It's all relative
On the other hand, this is a resort, this is Disney, this is vacations, somehow it's "supposed to" be more expensive. (not that it's right or "normal" but it's the way things go on vacations)
We know Disney is expensive in every aspect. It's part of a budget. Wether it suits our need or our budget is something we consider in advance.
But you can't really compare a meal outside of WDW and a meal onsite.
Eating OFFsite (when you stay ONsite) means you need a car. (of course a car gives you the opportunity of going places (universal, seaworld, malls, outlets ... and to spend even more money)
but if you get a car to specifically go eat offsite, not only will you lose precious time, but you'll also effectively add £30 or more to your TS meal if you do one per day.
All in all you'll pay the same price as the Disney price, but you might even pay more because eating offsite will ring the "it's cheaper" bell inside your head, and you might get tempted by an appetizer or another drink ...
(on the other hand, staying offsite to eat cheaper mean that you'll eat at Disney's more often than you care to do, because it's difficult to get out of property for lunch and go back, and you need to pay for parking, but this is another story)
On a personal level, I don't compare the prices of offsite vs onsite when it comes to restaurant. I consider the convinience of being onsite, and even if it's more expensive on property, the benefit of being able to stay "inside" often outweighs the higher price.
It's expensive alright, but we know it in advance and we can't be caught off guard, so I guess it's ok