That's true
(though I also expect mods adding leaders for all civs - but obviosuly with static images, not animation and sound)
but honestly that's something that have always been far smaller problem for me than civ switching - mainly because
1) Most such games (age of empires, paradox, other 4x etc) felt fine without
any leaders anyway, I shall survive with "only" like half of (seemingly much more) civs having their historical leaders now - especially as it opens the door for...
2) Sure leaders for every civ are great, you know what's also great? Civ7 with the new system finally being able to acommodate civs such as Missisipians, where we had absolutely zero chance of figuring out their leader and hence they could never enter the series before

3) As well as the opposite possibility: of "civless leaders" such as Tamerlane, Bolivar, Attila; or Charlemagne entering the game while avoiding the endless debate of whether he is "French" or "German" (and the undesired Franks/HRE civ ghetto), and being able to lead any European civ, like the Father of Europe deserves to. Another good example of this opportunity is Saladin and the avoidance of the endless pain of him being Arab vs Egyptian vs Syrian vs Kurdish vs "Ayyubid" civ leader.