Several points for you to consider.
In peacetime the main task is to intercept, identify and escort intruders, lost airliners etc - a task best served by an interceptor sized aircraft.
In war BVR can be constrained by ROE meaning a possible target has to be identified, either visually or by other means; and if they are hostile a bomber sized aircraft will be detected, identified by them first if they are smaller and able to give their weapon a height and speed advantage.
Bigger means less numbers and if the enem6 split up, use height splits, ECM etc the chances of a single large missile carrier achieving kills plummets.
“Missileer” aircraft were looked at during the Cold War by the USN* and the RAF briefly considered a Vulcan carrying Phoenix or Sea Dart** missiles etc, but none proceeded past the concept stage once modelling showed they lost out vs more fighters.
The US NGAD and FA-XX will be larger to be able to deal with trans-pacific ranges and mother aircraft carrying CCAs to the combat zone may appear, but I don’t see Missileer sun the mix.
*
https://en.wikipedia.org/wiki/Douglas_F6D_Missileer
** https://www.secretprojects.co.uk/thr...can-adv.17083/