Opinion: Counter Shield is 1 of the most innovative and impressive tactical maneuvers that Ash has ever utilized in the entire anime
It was a big flop in the Lake Acucity battle and wasn't much effective for Ash or Paul in the League either. The way this particular strategy was hyped throughout mid-DP seriously made me think like that this is going to be strategy/technique which will ultimately be the key for Ash to finally defeat Paul, who was handing over Ash embarrassing defeats one after another in DP. It worked wonderfully in the Gym battle against Fantina, raising hopes/hype for this supposedly amazing looking strategy/technique.
And then came the Lake Acucity battle, where this strategy/technique badly flopped and Paul handed over Ash one of his most embarrassing defeats ever in his life as a Pokemon trainer. It made me think: really? Such a supposedly creative looking strategy/technique, which made me think that this could be the key to ultimately trouncing Paul, was handled this badly in the anime?
The technique looked so cool apparently and so much creative, could have been handled so much better in the anime, like helping Ash in key battles with Paul, and...... ultimately amounted to squat. And saying that Paul himself used it later in the SL battle also doesn't mean much when it was hardly effective when Paul used it.
So overall I'll say: Counter Shield is one most overhyped, flop and badly handled techniques in the entire anime.
Opinion: I think Sawyer was a really good rival, Ash's third best rival(after Paul and Gary) in the anime. It gave an unique thought/idea about a rivalry where the rival would look up to Ash as a mentor, as his role model. It sort of gave a feeling that Ash's battling style/techniques are really that much good and worth something when someone is really looking up to it, trying to learn from it and inherit it in his own battling style to become better in battling. It gave a feeling that Ash as trainer/battler is actually that much good.
And I also don't think that Sawyer's growth rate in his rivalry with Ash was absurd or DEM. Sawyer started off a rookie who can hardly battle or rather knew much about it, not naturally the most gifted battler either. But one thing was noticable: he was hardworking, he clearly had the will and dedication to become better. He always tried to learn from Ash or rather every battle he had/saw, which also shows how studious he was.
So, though he wasn't a naturally gifted battler at all, he was very hardworking, dedicated and studious, willing to learn from everything, so for someone like him, the progression wasn't unbelievable either. And it isn't that his progression was too badly depicted either:
When he had his first battle with Ash, he could barely even put up even a reasonable fight, but was willing to learn from his mistakes.
When he battled Ash second time, his gradual progression was believable. His first 2 Pokemon were curbstomped, but his Sceptile had improved a lot. He used Greninja's battling style against it, and had it on the ropes, until the Ash-Greninja transformation activated and curbstomped Sceptile.
In the third battle, people could argue that his progression was unbelievable, but I don't think so. In his previous battle, only his Sceptile was shown to have improved, so this time it wasn't unreasonable for the rest of his Pokemon to have improved too. He defeated Ash's first 2 Pokemon, and then defeated Greninja to beat Ash, but there was one thing: Greninja couldn't transform into Ash-Greninja due its mind not being in sync with Ash. So by now, Sawyer was a trainer who can go toe to toe with Ash and beat him on any bad day for Ash(like that one).
In the League afterwards, it was thus very much believable than he was very skillful and strong trainer with a Mega Evolution who studies his opponents hard and skillfully produces apt counters to his opponents Pokemon during the battle, which he did with Ash in the League, and was able to give him a close fight.
Overall, I was really impressed by Sawyer as a character who despite being a rookie, not a naturally gifted battler, through his hardwork, dedication and willingness to learn from everything, became a skillful trainer who hard-counters his opponents Pokemon from beginning to end in a battle and made it to the KL semis. His overall gradual progression as a rival was well presented as well as Ash's role as a mentor to him.