naw man he's kinda right, despite his horrid comment history. hu tao teams' strength is single target and she's best used there. adding a barely-buffed xiangling to the team (realistically she only has noblesse and pyro resonance) plus she has higher ER requirements means that she does kinda average personal damage in single-target scenarios. in AoE scenarios, you'd do okay damage on one enemy and the rest getting hit by pyronado and don't have hydro on them will probably get hit with something like 13k on a crit. plus, if you actually record your footage (watch zajeff77's funerational video on youtube) you'll see that you'll miss some vapes on both xiangling and hu tao, but double hydro just applies so much that hydro aura will be reinstated very shortly after losing it.

now extra damage is always appreciated, but think about opportunity cost. what else could you be running in that team? it's more of a credit to the hu tao-yelan-xingqiu synergy that xiangling works there as well, but i wouldn't call her BiS as a 4th member. archaic petra zhongli makes you unkillable, and gives 20 res shred plus 35 dmg bonus for your yelan and xingqiu. kazuha gives you light CC (although kinda wasted in single-target environments) and 30-40 hydro dmg bonus (can't double swirl in hu tao double hydro teams). fischl provides good electro single target damage and access to overload which hu tao likes, what with her decent amount of EM plus you probably leveled her to 90. besides you're mostly playing immobile bosses with hu tao teams anyway so the risk of pushing enemies out of reach with overload isn't an issue at all.

plus, it hogs both bennett and xingqiu in one team. there are many teams that don't run bennett, and there are many teams that don't run xingqiu, but cutting both of them out at the same time makes your 2nd team significantly more limited (which one of the problems i have with raiden national).

zhongli or fischl wohld be better in single target scenarios. if you're playing an aoe challenge, just ditch hu tao altogether and use the other national teams.

of course this all assumes that you have built all these characters and can substitute them with each other at the drop of a hat. if you don't have any other characters for your hu tao team, then sure, funerational will easily clear single target challenges, much like every other hu tao team.

tldr: hu tao excels at single target, let her teams focus on that. xiangling's aoe dmg is better used in different teams.