They want to focus on BHX, MAN and STN
That bit is certainly true and why they bought the TCX slots at BHX and MAN. At BHX there is still capacity to be filled on Med routes (and plenty of terminal capacity) after the demise of Monarch in 2017. Jet2 have done a fine job of doing so and have further growth plans for BHX, fleet size permitting. I believe the plan was to get to 20 based aircraft by 2022, this has now changed as a result of the MAX issues.
Other bases like EDI will also continue to see Jet2 growth but the main focus for growth (particularly new destinations and additional based aircraft) will be the aforementioned airports. EDI was not considered by Jet2 for the launch of LIS flights in 2020.