No-one is saying the terminal doesn't need improving. Bother the read the history and you'll see everyone is saying the same thing. But the idea, it actually can't be improved is odd given recent history. Indeed, ABN-Amro, Barclays, Balfour Beatty, TBI, Bridgepoint and others were all prepared to put significant amounts of their own money forward on the basis their detailed appraisal of the airport potential suggested the complete polar opposite of your own appraisal. Indeed so far off the opposite end of the scale that the winning bid proved to be a UK record in terms of the price to earnings relationship of an infrastructure asset (about 30 times earnings) a clear indicator of the potential they believe to be there. This before they spend £70m upgrading the place.
That's no guarantee that they are right and you are wrong - only time will tell on that one. Nonetheless, you'll understand why the consistent professional opinions of 5 individual investment companies and airport operators will be taken as a better guide than your own. Ultimately it's a private business, receives no public subsidy (and didn't do for 2 decades before the council sold it) and its fate, as just like almost all businesses, will be determined by market forces. No one is forcing anyone to do anything against their will here. Consumers have a free choice. Airlines have a free choice. The owners of the airport have a free choice. No forced hands, no subsidies, no council or government handouts. Just a business that will either successfully serve local demand and will thrive or one which won't and will struggle. Hard to see what anyone's issue with that could be