Here we go again!!! The EZY 319s are 22k thrust per engine with a ZFW/APS around about 41 tonnes, the 320s have 27k engines and surprisingly have a ZFW/APS around 43.5 tonnes if I remember correctly. The high 319 weight due to the 156 pax requiring a beefier centre fuselage with the extra overwings i.e. the same as the 320, just a fuselage plug missing because of the shorter length.
Thus the 319 is take off performance limited and fuel tankage has nothing to do with it. If the 319s had more thrust pinned in ( its the same engine after all) then they would have no trouble with the longer routes. The extra pax on the 320s are more than made up for by the 10 tonnes of extra thrust (156 pax against 180).
The 321s are supposed to depart this autumn - I presume a buyer has been found for them??