I honestly can't say a lot about Nando at all. Even though he's appeared more in Season 10, we've seen him more along the lines of his Contest progress. From a Secret Sphere of Influence, all we heard of his Gym progress was "I've only got one Badge so far." At least we've seen him in the Hearthome Contest, but that's all?
After he vanished during Season 11, Season 12 (besides his TV appearance), he then appears right at the start of the Grand Festival preparations. Its just like he was only made for his appearance in the Grand Festival, after Season 10 aired.
If we were to have more episodes of Nando between 2 full seasons, I would have more views on him. I just feel bad for the guy with his treatment on the show. Seeing him with some beast Pokemon like Altaria, Lopunny and Armaldo is amazing stuff, but only shot for 1 appearance each. At least he left with a great position in the Grand Festival, landing in the Top 4; along with a great semi final battle with Zoey.
As for Gym Battles/League, really... sad to see he lost in the first round (to Ash) of the Suzuran Tournament. But when they were matched up for the first round battle, its not so surprising.
Perhaps the dedication to focus on both Contest and Gyms was a bit too much to work with on screen?