Troop experience. Is it necessary or not?

Well, troop experience is not a mandatory feature at all. It changes the balance of power quite significantly. As for me, ideologically I'm in favor, but I wouldn't add it to SoD. Let these be features of mods like WT, along with other perks. Otherwise, one could actually pile a bunch of things into SoD and end up with WT. And that is not necessary.