Aria is very easy if you go the affection route. It's because the game is very badly balanced for the punishment route. Even for less difficult girls like Rebecca the time you would have to spend trying to break her through punishment and forced bondage is pretty long, even basic things like threaten result in a heavy affection loss and that is when you pass the manipulation check. Unfortunately the chance to do anything depends heavily on the affection. Basically no matter what you do breaking the slaves using logic and psychology doesn't work in this game, you have to know exactly what actions will give results and what actions to avoid.
On the other hand if you go the affection route you can zero Aria's willpower in few days, you only need a combat party capable of doing her quest, simp some money at the end and you can go seduction, raise some arousal, dominate-> get undressed, abort, inventory->wear something, repeat until she's out of stamina.
Well I do agree about punishment route, for now it's just not worth it. The new mechanic defiance and fear was supposed to change things, but still, love route is simply outmatching it in every aspect. The girls, won't run away, you can leave them be and don't need to constantly maintain their mood in case they decide to do something stupid etc. I didn't play much using harsh methods, but when I got Rebecca, I didn't want to go easy on her, so I decided to test new mechanics. For the sake of role-play, I wanted to teach her a lesson and didn't want to abuse game mechanics. Even though, I broke her willpower in the end, it still took me much more time, than it would be with love route. The thing is, I dropped the idea to constantly harass her and started to bring her on dinners, and even arranged horse riding with top gear. And after I started to do that way, I lowered her willpower really quick. So yeah, it's need to be heavily balanced. I didn't get Aria, because I didn't want to grind for this ridiculous 75k, but I hope at the time new content come, harsh route will be rebalanced, so I could use different methods with her.
Speaking of abusing game mechanics, I think the event with bathing with slave is one of them. You can go bath almost as many times, as you want. Using dominant option, you lower slave willpower pretty quick. It's almost ridiculous how I managed to lower the willpower of almost all of my slaves just by making them scrub me