Maybe you should actually read the conversation I was having. We were specifically comparing whm and sch single target healing capability. Regen was compared as part of how much cure potency each of the two jobs have over the course of ~45 seconds.
Also, SCH doesn't get a free medica II every thirty seconds. They get a free aoe regen. It doesn't come with the upfront 200 potency heal that Medica II. Not saying it isn't a good ability, either, but it's not Medica II.
And no, Adlo shouldn't need to be compared to Cure II. The problem is that Adlo *is* the Cure II for SCH. This was fine back in 2.x (can't really comment on 3.x since I played WHM in 3.x instead, but it felt fine recently when leveling sch 51-60), but now it's just got far too high of an mp cost for far too low of an effect, especially since they also nerfed SCH's mp sustain. Overall, that's not necessarily a bad thing, as it still works well for an ability to cast before the pull and occasionally for topping off a tank's HP while also giving them a little extra, though it's best use now is for throwing on someone (especially a dps or healer) right before a big hit is thrown at them (easy example being the charge the first boss in Bardam's Meddle does) to mitigate it.
Crit adlo is awesome. Always has been. It's also almost impossible to get it to a higher rate than 1 in 5, maybe 1 in 4, and that's when you can actually optimize your gear for crit rate. This was less of an issue when you could pretty much spam Adlo, but now you have to use adlo very sparingly, so you rarely get to see a crit out of it. It's absolutely spectacular when it happens, but it's far, *far* too unreliable to actually count on, tying the bulk of Adlo's usefulness into RNG, such a strong usefulness when it *does* happen that they find the need to keep the non-crit effect very low. "Can whm 20k shield on someone?" No, but neither can SCH with any reliability.
All of this would be much less of an issue if it didn't effectively limit us to spamming a weaker Cure I to keep people alive. You say Adlo serves a different purpose than Cure II and you're right, but we really don't have anything to compensate for lacking a Cure II. Adlo used to, but it doesn't even come close to doing so anymore. Lustrate/Excogitate are the closest, and they definitely help and are in general good abilities, but they're gated behind aetherflow stacks and Lustrate itself is weaker than Cure II. Sure, you can spam three in 3 seconds for a very nice burst heal, but then you're down all of your aetherflow abilities until the aetherflow CD is up, or you consume your fairy and lose its healing for 30 seconds, and it still doesn't compensate for the fact that whm can easily just spam Cure II without running out of mp while negating 700 potency worth of damage taken every gcd, while sch is stuck spamming a 400 potency Physick with the occasional lustrate for 600 potency and an excog once every 45 seconds for 800 potency. That average potency comes out to a good deal less than the 700 potency WHM can do, and the fairy's 250 potency (though significantly weaker than this in effect due to the lower stats fairies have compared to us) every 3 seconds isn't enough to bring that average up, especially when you add in the whm can keep a 150 potency/3 seconds regen on top of already doing sizably more healing than sch.
Sustain also carried the advantage of not requiring you to target your fairy to heal her. Yes, physick can heal about as much and instantly, but you have to target your fairy first, which is less of an issue in 4-man content, but is far more of an issue in 8-man content, since you can't just hit an F# key to target her quickly. You could also use sustain when she didn't need the full physick potency and it would most likely still be healing her when she takes more damage. As for placement, that only does so much, and isn't really very possible during large pulls in dungeons where aoe's flying around randomly because of the tank constantly having to move to avoid said aoe.
SCH's not useless, and I'm sure it can do the content, but it's definitely weaker than the other two healers by a good deal, and it's not in a *good* place right now. I don't think it would take much to get it in a good place, though. Return Embrace to 300 potency and give Physick another 50 potency (maybe even 100, but that *might* be a little too much, not sure) would be the easiest ways to fix it. Giving sustain back would be a great QoL improvement, so we don't have to worry about having to try to target a 9th party member, and SMNs need it back even more, since they don't have the option of targeting their pet and casting Physick on it for ~25% of its HP, and it's especially a pain for any of the healers to need to try to keep track of the HP of a pet not your own, much less targeting them to heal them, and can potentially make for healing a 10th/11th/12th/13th party member (not that you're likely to have 4 summoners lol) if we do try. X3
Honestly, I feel like one of the problems SE had when pruning away "rarely used" abilities is that they focused too much on the usage statistics and didn't fully consider context. Far too many SMNs and SCHs completely ignored their pets' HP and never bothered using sustain (and there's plenty of opportunities in most content to use sustain without reducing your dps) even though they should have been using it. If they adjusted the usage statistics to rule out bad players who just don't bother using an important tool, they'd have likely chosen to keep Sustain in the game. They also clearly ignored how important it is on smn for solo content.