Jet2 738, as your detailed research confirms that the majority of the new routes are operated by 733 - which is a finite resource - can you advise which routes are being pared back to accommodate them?
The B738 fleet has shown some healthy growth. In 2014 6xB738s were acquired and in 2015 another 4xB738s. Inevitably the B738s will be taking over routes from the B733s, so that new and untried destinations can be allocated to the B733s to test the popularity of the new routes with fewer seats on smaller aircraft.
Although there would appear to be plans to order new aircraft, these would not be making an appearance for at least another two years. In the meantime the present policy of buying or leasing B738s, when the price and conditions are favourable to JET2, could be expected to contiinue.