I’d say Thoth is equally good/bad in any position, he is kinda position-independent. In War with Field Aid, he can be a royal PITA in the Endgame, so maybe he is more suited for wing position in this case.
I’d love to see more teams with Thoth as a tank to practice my tactics against him.
I wouldn’t call any slow hero a “great tank”.
My current understanding of the raid tactics is that most raids can be split into 3 stages, like in chess:
During this stage, attacker tries to destroy the tank, while defender needs to survive long enough to charge their flanks/wings. Almost no specials are fired during this stage, so most damage is done by tiles and Fast/Very Fast heroes (and Average for the tank), and defence factors are mostly troops, raw defence stats and innate abilities (resistance).
Kunchen plays a good role as a tank in this stage, because he has high defence and resist to defence debuff. But usually tanks do not survive the Opening, so his special is 90% irrelevant because he is Slow.
Thoth could play better here just because he can charge faster and deal more damage before he dies. He has less defence, of course, but if he charges, he is much harder to kill by tiles only.
This is when special abilities of the heroes start to play, and synergy between abilities can be exercised.
Attacker’s goal is to exploit holes in the defence to ghost the tiles to charge heroes and get rid of unwanted tiles, and kill most dangerous defenders.
Defender’s goal is to kill as many dangerous attackers as possible while keeping as many heroes alive as possible.
Slow tanks and flanks, and average wings are able to cast their special during this stage. In attacking team, heroes that attack 3 targets will only have 2/3 (or 3/4 in case of “minor damage”) of their efficiency.
This is when Kunchen shines. He is an ultimate middlegame player, leaving the other team defenceless and healing his team. But he cannot be in the tank position for that, and cannot be at the wings, so only flanks.
Thoth will be active during this stage, in flank and wings position, but his impact is negligible. He has no additional effects of his attack, and doesn’t deal enough damage.
Endgame is a stage when most dangerous heroes are out from both teams, leaving one or two heroes on the field.
The goal for the attacker is to just finish off the remaining heroes, while defenders can also stall the game until the time runs out.
During this stage, usually one or two wings of the defender team are alive, and attacker team can also have only one or two heroes available. AOE and 3-target total damage is greatly reduced, as well as the tile damage, because you can only hit the wings with 2 columns of tiles instead of 3.
Kunchen’s efficiency is very limited at this stage, because he is slow, and has very low raw attack. He is not a threat, and the only way he can win is when attacker has no snipers left. So I would not recommend placing Kunchen into wings at all.
Thoth-Amun will have reduced damage at this stage, but he will have much greater survivability than Kunchen if he is left at wings.
Fighting against Thoth-Amun during Endgame is a nightmare.
Best place for Thoth is wing or tank position, best place for Kunchen is a flank or tank.
You are free to apply this analysis to any hero pair you want.