I own Lilith and Alice.

Your point about Sammy being a bad example is right, and I could have made the counterattack distinction more clear, but the rest is incorrect. Lilith's got high reflex versus most standard mids (save very few people like legends or Sammy), and reflex totems or proper stones can easily account for the difference.

Let's compare them all, one by one, since you keep insisting Lilith is so much worse.

ACTUAL GREAT ones like -100% speed and defense for 5 minutes single target

Single target versus whole team. Of course the single-target is going to better. Now, the advantage Serestia's Expel has here is that all she needs to do is block versus a counterattack, which is much easier to arrange, and with that massive speed and defense debuff your entire line will probably get a chance to attack the weakened target. It's a very good chance you will be getting the ball. Advantage: Serestia.

and -30% attack power and crit rate for 8 minutes enemy team

I'm not sure what you're talking about here, this doesn't exist. Dark Eden? It's 10%/10%, not 30%/30%. That's a very big difference. -10% crit rate and power is very nice since any action will trigger it, but it's probably the last skill you would max on Serestia. Advantage: No one

up to -30% enemy team reflex and max hp for 45 minutes

This along with Expel is Serestia's true power. However, she needs to stack 3 actions together to max this out, and action speed is generally dark's weak point. To realistically max this out you need to build an action speed mid (or back, or wherever you have Serestia), which involves Serestia/Alice or Avnore/someone off-color like Kiki, since action speed is not dark's strong point. However, it's rather unfair to just assume someone will have both Serestia and Alice to make this work better, then compare 3 actions with Serestia to just one of Lilith's. Advantage: apples and oranges, not fair to compare Lilith's one counterattack debuff to x3 Serestia actions stacked together.

upward stacks of -40% crit rate AND reflex for TEAM for 45

LOL You're just going to assume that you're gonna get Alice 8 turns? Alright buddy. I'm not gonna do that, I'll take the weaker non-stacking debuff that is much easier to trigger. Advantage: Lilith.

-35% max hp -35% reflex -20% crit -20% speed for line debuff totem permanently

Yup, Alice is great. What's your point? She's a true debuffer, every single one of her passives and her active is built around debuffs. Lilith has a passive for stealing, a debuff for counterattacking, an active to make her stronger, and a line totem to make entire line sturdier. She's a swiss army knife, Alice is pure debuffs. Of course Alice's debuffs are going to be stronger as a result. Advantage: Meh, Alice? I feel cheap saying that, again it's two completely different things.