You seem to be ignoring the huge change in playstyle and though process after the rework…
I’m not really keen on explaining something long so I’ll just link a thread that explains it better:
TL;DR: Basically what I said, her gameplay has changed. I don’t really know what you mean by mechanics besides just her ability to heal staying the same but I will say, her heals were modified and her heals are just 1/3 of her kit. If it’s GA you’re referring to instead, again, it’s just 1/3 of her kit.
This is really dumbing down the changes given to Mercy. It wasn’t simply just putting her ultimate on a CD. Significant changes were made to it. For example, it’s on a 30 second CD (longest in game), has a radius of 5 now, can be interrupted, has a 1.75CT and doesn’t grant invulnerability. All of the above will definitely affect the fun of playing Mercy.
Same for her heals. A 16.6% decrease in heals is huge, in the context of Mercy, as she only had 60 heals to begin with. Thus, 50HP is much more noticeable and the fact that you’re spending way more time healing a single target, mainly tanks, just overall makes her gameplay more bland.
Now, here’s the biggest thing that makes Mercy inherently different to Mass Res Mercy. Yes, it’s Valkyrie. The 15 second, glorified spectator mode where you either become a mediocre Orisa Ult or a temporary Moira (AoE heals). Once again, another thing that would drastically change the fun aspect of Mer,y.
Literally not what this is about. Otherwise, you wouldn’t see people complaining about current Mercy or also don’t want mass Res back. I for example am fine with letting mass Res go but am definitely not keen on current Mercy.
Ah yes. Her gameplay has definitely stayed the same. Besides of course her ultimate, her base kit and her new e ability. Other than that, sure everything else has stayed the same. 
Nope. I rarely even used mass Res for anything besides 2 man Resses. I found old Mercy fun because of the idea of getting rewarded for surviving. I always found the survival aspect of Mercy fun. That has irreversibly been tainted by Valkyrie which gives you training wheels for almost all your abilities.