I could not mention all of the potential synergies obviously, but I cant stress enough the burn to mention one, and top that with JFs Dot damage and Telluria will almost look like fuel to the fire than a healer. Heck, put in Guardian Falcon as well, and you have a firebomb even with tiles alone if you will.
However you had a really good point with Kunchen, who could lose out on potential healing if he heals a team with little damage done to them. But this got me thinking… If Telluria heals little each turn to a team with minor damage taken, and Kunchen heals best to a team that have taken major damage. Then this shows that Telluria would works best for an already strong damage resistant team. While Kunchen protects and brings up a more squishy team to higher potential than Telluria could.
Telluria or Kunchen might show their true potential at different tasks. The actual reason Im sceptical against Telluria is not because her abilitys are bad in any way, but that they seem to be spread to thin just as with Neith. If a hero got little of each, it then often turns out to be a mediocre performance because no abilitys that effect you will ever be overwhelming enough for you to counter. I think Telluria could shine with help of another healer, but not so much on her own.