No need for live food though. Mine have all grown quickly and healthy with proper water changes (70% every 4-6 days) New life spectrum pellets, Tilapia filet , shrimp , some squid some silversides. Variety is a big help as is water quality.
I think its a bit invidual! I have 5 senegalus and 2 endlicheri and every one was and is the same size and have grown like at least 15cm in 5month. Except for one edli he has grown like 4cm but he is always eating so nothing wrong there.
i've got a similar experience. 7 months ago, i bought a senegal and endli. both are roughly the same size at around 3". today my endli is already around 10" and my senegal is still the same. hasn't grown at all literally. both are fed the same food.
My endli i have had or three weeks that started at 3'' is already at about 4 lol it must be in the water becasue my fish grow so fast its not even funny