How I use Telluria and how I want to use her?
In PvE. She is pretty strong PvE healer and actually can help to finish legendary level of challenge events or those difficult quests like Springvale or costume quest even on 3/70. Mana slow in PvE is less relevant, because you can bring LJ or Mist to achieve better results (I actually use Mist if I need mana slow).
In raid offence. I usually run 3/2, and my main color is purple with C.Rigard, Tiburtus and Sartana.
If I need a green 2, then I take Telluria and C.Melendor, and those 2 synergizes pretty well (even with HoT override). Yes, sometimes I can take LJ or Jack O’Hare, but if I have Telluria and C.Mel, and you run C.Mel after Telluria, you can get +Def && good HoT && minions && dispel in one. Then purple trio just finishing main 1/2 threats.
In war offence. My green mono consists with Telluria, Melendor, LJ, Caedmon and Jack O’Hare. She is also pretty good support healer and can win matches by herself. I won one match when I have one Telly standing vs 3 enemy heroes on healing war. Most problematic was war timer actually, not Rigard and Khagan in corners (they was alive with my Telly. The rest of my heroes was killed by unnecessary green crystal runned to Boril tank under his buff). Mana slow was cleansed almost every turn - but still no problem on offence. I was lucky to kill Khagan on last seconds of war match, there was a shot.
On raid defence. I personally do not use Telly on defence often, because for my (Platinum) level she is insanely OP, and I constantly pushed to diamond, where I cannot raid effectively now.
On war defence. In our alliance we run a blue tanks, and I currently use emblemed Boril for tank, and Telluria as flank and Vela on wing. Often Telly on flank was a last man standing. I do not want to run one of my 4* in place of Telly.
I want to continue to use her in situations 1,2 and 3 as average heal-all 5* hero. Even with her crap heal (only Tarlak heals less) she is very useful in that role.
I do not want to use her in my raid defence, because I do not want to be pushed to diamond by an OP hero without proper attack teams.
I want using her in my war defence just because I do not have Lianna or another good 5* fast shooter. When I got Lianna (TC20 running), I will use her in my war def instead with blue center (Vela finally replaces Boril then).
So, I do not want a OP defensive hero, I want an universal healer hero with good defensive capabilities. And Telly perfectly fits my playstyle now and I want to retain this playstyle.