A few people used Karrablast for the dark horse project way back when Ashley11 was still alive, and they had really nice things to say about it. Of course, Fletchling wasn't nearly as popular back then, so C- or D would probably be a good place to leave it for now, and further testing could probably help to decide if it's worth moving up.
I don't have much experience with Gothita, but I don't think it should be any higher than Wynaut, who I would imagine performs really similarly, so B- would probably be a nice place for Gothita.
A few proposals of my own -
Foongus for A
Even with the ubiquity of Fletchling, Foongus is a phenomenal pivot, able to effortlessly fit onto a variety of defensive, balanced, and even some offensive teams. Its good defensive typing and access to one of the best defensive abilities available in LC allow it to check a huge number of threats over and over, including Chinchou and Carvanha, and it can be a nuisance once it's in thanks to its status moves. Hidden Power Fighting allows Foongus to win in a 1v1 situation against non-Eviolite Pawniard outside of Iron Head flinches, and a key resistance to Fighting-type attacks makes it a brilliant check to potent threats in Timburr and Mienfoo; this is made even better by how Foongus is able to switch in on these Pokemon repeatedly due to Regenerator. It is able to take the Fighting-types on even when missing its Eviolite, meaning it can act as a pseudo-Knock Off absorber, working especially well with a Mienfoo teammate of its own; the two of them together can take on nearly every common Knock Off user, and because both have Regenerator, can do so throughout the match. Foongus's premier counter, Vullaby, is hardly ever seen, leaving a large number of teams quite Foongus-weak. Fletchling isn't able to switch in on Foongus because Sludge Bomb usually 2HKOs, while Acrobatics does not OHKO, on top of a possible Spore if Sleep Clause isn't activated. Overall, I think Foongus's strengths are notable enough that it is at least able to pull its weight as much as Scraggy or Dwebble, if not more.
Spritzee for A
This one I am much less certain of, but I'll give this a shot anyway. Spritzee has a ton of utility, as we all know, with Wish and sometimes Aromatherapy; it is also a good win condition for defensive teams with Calm Mind, because it still maintains a lot of utility early and mid game. One really nice boon to the Calm Mind set is that it is usually able to OHKO Choice Scarf Pawniard with Moonblast after a layer of Spikes, while Pawniard fails to OHKO in return with Iron Head. Although it doesn't appreciate Knock Off at all, it is still able to usually handle a good number of popular threats without its Eviolite, such as Mienfoo and Scraggy; there is also the option to simply pair Spritzee with Knock Off absorbers, such as the aforementioned Foongus + Mienfoo core. Spritzee is a staple on many bulky fairy+normal cores, a core which is able to check a ridiculous number of top threats in the current metagame due to high statistical bulk of both members, and decent offensive presence for both. Spritzee was at one point frowned upon; this is because its lack of versatility means it really has trouble adapting to unfavourable metagame changes. However, I think that at this point, the metagame has changed so that it favours Spritzee with its statistical bulk and typing, enough to warrant a placement in A.
Magnemite for A+
Another proposal I'm not completely sure about, but I've been having a lot of success with Magnemite recently. Hazards breaking Sturdy were once considered a really big issue that completely held Magnemite back by forcing hazard control support to be used alongside it; said support is still preferable, of course, but with the rising popularity of Endure, Magnemite finds itself often able to still take advantage of Sturdy to check boosted threats as long as its Berry Juice is up, even if it isn't at full health. Magnemite is an excellent safety net, similarly to Focus Sash Abra, but unlike Abra, its numerous resistances and higher statistical bulk allow it to actually switch in on a lot of things. Magnemite's typing in particular allows it to shut down a number of defensive Pokemon, such as Spritzee and Cottonee. Another huge advantage Magnemite has over Abra as a safety net is its ability to utilize Volt Switch, granting its team a great deal of momentum. I find Voltturn to be an extremely potent playstyle right now, and Magnemite is one of the best options available for it due to its aforementioned traits. There's also Scarf Magnemite, which can hit switch-ins hard with Analytic boosted attacks, maintains momentum as well through Volt Switch, and can revenge-kill a lot of Pokemon; more importantly, a lot of the checks to Sturdyjuice Magnemite will be hard-pressed to avoid the 2HKO switching into Analytic Magnemite. Overall, I find Magnemite's ability to consistently pose as a significant threat to almost all team archetypes while functioning effectively with two very different sets is enough to place it in A+.