Well, I have to agree that Gothitelle makes it too easy for a Heracross/Darmanitan sweep, and even easier if you have a team built around Gothitelle.
The only things that can really wall Darmanitan in the first place are physically oriented bulky waters (Slowbro, Suicune, etc.), Pokemon with Intimidate (Defensive Hitmontop, Arcanine) and stuff like defensive Rhyperior. Only bulky waters are a surefire counter as Arcanine, Rhyperior and even Swampert are still outsped and 2hko'd by LO/Choice Band variants.
A team without any of these is toast as STAB Sheer Force Flare Blitz will kill 2-3 Pokemon before recoil takes Darmanitan down.
Heracross is arguably harder to beat defensively due to its STAB moves. Only bulky ghosts are truly safe, especially from the Choice Scarf variants, which generally carry CC, Megahorn and Edgequake and are pretty much impossible to wall without proper prediction and/or sacking a team member. LO and Flame Orb variants aren't as good, because of that base 85 speed. Great wallbreaker, but doesn't sweep.
Gothitelle has an interesting niche here. Trapping and eliminating bulky waters is awesome, because once it does so Darmanitan sweeps like a boss. On the other hand, it actually deters Heracross slightly as nobody is going to Choice-lock themselves into CC while Gothitelle is still alive, allowing you to counter it with something that doesn't take such a ridiculous beating from Megahorn.
Overall, I'd argue that it's going to mess up the metagame, simply because it makes HO so much more deadly, and Stall so much more junk.
Edit:
Also, FlareBlitz,
It's true that Gothitelle will never sweep. It's also true that it seriously deters choice users because Gothitelle CAN revenge kill a large portion of the offensive metagame. It's also not a 1-trick puppy; it can come in more than once, possibly to trick off a Choice Scarf/Specs. I completely agree that a Pokemon as completely mediocre as Gothitelle can be replaced with something more deadly, but not always.
My team, as an example, heavily relies on an offensive core of Darmanitan/Roserade/Kingdra with Togekiss as stallbreaker. My worst nightmare with this team is facing either RegiBro or a defensive core of Ferroseed/Suicune, who can swap around, playing around Choice Scarf Darmanitan and generally not giving a shit about Kingdra (+1 Outrage doesn't 2hko Suicune) OR Roserade. Nasty Plot Togekiss at +2 3hkos both cores except for Registeel, who is 2hko'd by Aura Sphere, and can generally get a sweep if the opponent doesn't have a revenge killer (I played you once, didn't I, FlareBlitz?). However, even that requires a bit of prediction and playing around Leech Seed and Twave, as well as faster offensive Pokemon.
When I replace Togekiss or another Pokemon with Gothitelle, I end up being able to trap either member of the cores and hit them hard with the appropriate coverage move of choice, be it Thunderbolt, Shadow Ball, or a HP of choice. It can also trickscarf them, which cripples most defensive Pokemon. It may not have any use after killing its first target, but if Heracross is on the opponent team it deters it from using Close Combat in fear of a revenge kill, which otherwise wrecks my team.