Late reply, but I actually used a Thievul in an online competition that was for SwSh but with only Galar Pokémon. I used it alongside Indeedee-F in order to set up Unburden alongside Psychic Seed which would prop thanks to Psychic Surge. Indeedee would then use Follow Me while Thievul set up Nasty Plot, and suddenly you have a Double Dance in one turn. Being able to outside Dragapult and threaten it with Dark STAB is immediately so good. Outside of that, it’s definitely not great, but at least it has a very tiny niche and it could do something, so it’s far from the worst Pokémon.
And lastly, I like how the Nickit line is actually based on real foxes. My issue with the other fox Pokémon, the Vulpix, Fennekin, and Zorua lines, is that they are based off of kitsune, and not real foxes. Now I don’t mind kitsune, but they already used the concept 3 times already, and the Nickit line delivers a fox that is not a kitsune.