I think it's more than great to have a new way to level troops, and a reason to use loot for something other than money. The perks are not overpowered, at least in early to mid game. If you use your loot early on to level your troops, you will not only be paying what would be thousands in terms of denars, but also pay more when actually upgrading the troops, AND then pay even more through the daily wages of said troops. In that sense, I found that I prefer selling my loot rather than using the equipment on them. This same effect you would have seen if you played Vlandia with the past culture bonus (+20% troop exp from battles). I would never upgrade my troops early, maybe only one tier at most, because the costs of always upgrading your troops far outweigh the benefits.
For these particular perks, even when you are good economically, trust me, this will still feel like a big hit to your wallet if you do it too often. I was clan tier 4, I had -600 wages, and the 3 workshops that I had at the time got me somewhere to -100 daily. At that point you would still rather sell the loot than just use it for troop upgrades for no reason.
And late game, doesn't hiring clans cost literal millions of denars? Again I don't imagine you want to do this all the time. All in all, I feel it's really great having a new "money-sink", like we have been asking for before, and also a more active way to train your troops! Troops are very expendable, and currently a tier 5 troop isn't that much different from a tier 3. I wouldn't even say it's worth the money. At the moment, upgrading troops is mostly for roleplay purposes I feel like, for example I like having my Vlandian sergeants, they look cool. Do I need them? Not really, I'd be better off with an army of crossbowmen. But then, training crossbowmen is quite easy to begin with. So I feel the perks benefit infantry more (which have more mortality, unless they also have throwables, so I prefer not nerfing this perk in the way suggested above - "tier+3 troops don't benefit from it..." honestly, don't do that. With the leadership perk that pretty much upgrades most of your recruits to tier 2 from the get-go, the perk would really be useless. And also, the early tiers require way less experience to level your troops than the later tiers. Don't touch the lovely perk!).
Training your troops by killing looters all the time got really old, please don't bring me back to that! I'd rather choose to suffer through a 100% trader playthrough and then abuse the hell out of the new stewardship perks than continue doing that. And if you have the patience to level trading so much you honestly deserve it. I didn't even use the perks much, but just having them there as an option gives me immeasurable mental comfort, knowing that I won't be stuck all game farming looters for experience.
Turning these great perks into morale or reduced wages would make them very useless... For one, you are trading loot (=money) for reduced wages? Doesn't make any sense, it has no practical use. And morale no thank you, I'd rather defeat a party or raise my leadership, + have some other steward perks that do this, + treat my men in the tavern to some booze and wenches like good old times (= another money sink for the purpose of raising morale).
Don't ruin a good thing! The perks are genius, and we can finally say goodbye to our looter PTSD from farming them so much for the first time during Bannerlord development. I will never forget their faces! They're haunting my dreams every night! Take my loot now!