One of the major problems with the current design for the TP is that it bears very little resemblance to that proposed in June 2015.
Feel free to Google image search (other search engines available...) the renders from this time.
When looking at these, it is difficult not to have high expectations. The impression is of a completely new build terminal, which is light, airy and spacious. It provides a uniform look to the airport in a unique style.
When looking at the present design, and now the walk through, the impression is opposite to the above. The new terminal is actually a "bolt on" extension, with no apparent attempt to get a uniform external appearance. Certain areas look light, but the walk though gives the impression of a cramped dark shopping mall.
Expectations, set so high in June 2015, have tumbled accordingly.
It is difficult to say what the solution is within budget. Perhaps the terminal building can be expanded so that the floor space can be opened up more around the Central atrium. Perhaps it could be taller? All this requires another planning permission, and possible delay to the project.
There should be opportunity to deliver something of high quality. The airport is looking to attract high end airline customers. Also, the clientele on low cost carriers are not exactly the dregs of society. I hope a reasonable compromise is found.