Well then, how is it that the Tranquil lose the ability to *manifest* their emotions, lose much of their memory and lose sense of self-preservation or motivation?
They don't lose those things. During Broken Circle, the Tranquil in charge of the store room will refuse to leave it, even if you order him to, because he thinks he is safer if he stays where he is. He clearly still has survival instincts. He's not going to go running through floors full of demons and abominations if he doesn't think he has another option. And in Inquisition we hear from more then one Tranquil motivated to find places and ways to apply their (sometimes considerable) knowledge and live useful lives, even in a world that can't help but be freaked out by them.
The Tranquil may not express themselves the way they used to, but they still possess the things that are supposed to be taken from them. And, again, we don't know if these things are specifically linked to the Fade, or if they are just how the Fade pushes through to affect our world. Chicken/egg.
... But that only strengthens the notion that less Fade = more Tranquil, and that there are likely many levels people can be separated from it, with Tranquil being most severe. Solas, after all, tells us about how the Veil "cut most people's conscious connection to the Fade". Tranquility obviously cuts way more than that.
Tranquility cuts away something, but whether that something is really related to the Fade itself or if it's a sort of lobotomy that represses the things that a mage usually uses to control the Fade remains to be seen.
I'd be curious to know what happens if the Rite is performed on a non-Mage. There's a lot we don't know about Cassandra's vigil, but THAT doesn't involve lyrium, and the Rite does. Again, getting lyrium branded into your head doesn't sound healthy under any circumstances, but is that what makes Tranquil so... tranquil? Because if so, then the Rite just takes your desires and dreams from you, and doesn't really affect your connection to the Fade at all.
You also can't say that they "don't miss anything for it", especially that it's been established in the narrative that the Fade was precisely what made ancient elves so powerful and immortal, among other things.
Not saying the Fade doesn't sound like a great thing to have. Just saying it's a leap from that to the assumption that losing access to the Fade forever would result in everyone being made into vegetables. Life seems to continue on, Fade or no fade, and the Tranqulity only comes into it as as we mortals fumble to control how and when it gets used.
Not saying it's impossible that it would make everyone vegetables, mind, just that we can't treat it as an automatic thing. As I've said, I wouldn't put it past Bioware to make "must destroy all magic forever" the Dragon Age version of ME3's "must destroy the mass relays," ending choices. Here's hoping they handle this one better, if it comes to that.
You're missing the point. Solas is well aware what *actual Tranquil* is. His comparison should make you realize the extent of how Solas thinks the Veil is hurting people, by denying them access to something in their life he considers very important.
As I've said, he's in dire need of a reality check, both in terms of how insulting he's being and in the "you know, everything doesn't revolve around YOU" variety. After all, Sera insists she's just fine the way she is, and Solas can't talk her into feeling otherwise. All of the "elven glory" stuff isn't interesting to her. Solas might insist it's because people like Sera have no concept of what was lost, but I'm sure he'd rather believe that then consider that she might know exactly what was lost and still not care. The little people just trying to live their lives would, I'm sure, rather be left alone.