I don't remember Riolu using any aura in battle. Was it invisible? If so then we can't say for sure. Lucario could possibly have some BS but I hope it's Mega Lucario rather than A-G BS again.
No, Dragonite is stronger than Riolu as of now.
1.Bea defeating ML doesn't mean anything since we didn't see how she defeated her. Now, sure she used Grapploct in a battle since it seems it's an ace, but what is Bea used other Pokemon( flashback looked like it was on same stadium where Ash and Korrina battled ; so it was 2 on 2). Maybe it was 3 on 3, so it's easy to say that Bea's 1 Pokemon defeated 1 Korrina's Pokemon and that how it goes, so in the end ML had to battle Grapploct + 1 Pokemon. Now, if it's 1 on 1, sure maybe ML wouldn't win but it wouldn't be that easy of a match. I don't see how she find that since ML would definitely beat Riolu. It makes no sense that Riolu > Mega Lucario.
2. Dragonite had to battle Meinshao and ML and it beat them( thus Gengar helped a bit). Not to mention that: Grapploct spared with Chuck's Poliwrath( so it was 100% when it started a match with Pikachu) and battled Pikachu who despite inconsistent, Pikachu should always be strongest in Ash's team, so Pikachu > Dragonite( but Pikachu battled Hitmontop for a bit) and Grapploct took several hits from that, resulting in Grapploct was wounded and not fresh when he battled fresh Riolu. Ash spends and trained Riolu more than Dragonite but Riolu still didn't catch up to Dragonite it will when it evolves soon.
1. Your logic about number of Pokemon being used against Mega Lucario is simply irrelevant and makes no sense.. The point is, Bea didn't consider Korrina as a serious opponent. By your logic, Bea had to use more than 1 pokemon or a stronger pokemon to defeat Korrina's Mega Lucario. If that were the case, she wouldn't have considered her to be a weak opponent. The whole point here is Bea considered Riolu + Ash a more serious opponent than Korrina.
2. Lucario also battled with Gengar and defeated it so I don't see the point of claiming Dragonite had to also fight Mienshao. You yourself say Pikachu is inconsistent, and then state it is the strongest on Ash's team. This isn't true. Pikachu wasn't the strongest Pokemon on Ash's team definitely in Kanto, Johto, Sinnoh, Kalos and arguably in some of the other regions. A Pikachu that tied with a Latios in the Sinnoh League lost against Viola, the first gym leader in Kalos. Pikachu's strengthly is simply always inconsistent and should never be considered while comparing a Pokemon's strength.
On some days PIkachu might be > Dragonite, but on some days PIkachu might be < Ash's Farfetchd.
Claiming Grappaloct was supposedly weak cuz it sparred with Poliwrath before is just an awful argument.
1. We could easily argue Ash is not the kind of trainer who would exploit such an advantage, plus, Bea wouldn't use a weakened pokemon in a pwc battle. Plus, right before they battle, they take off their shoes etc, for all you know, we could just as easily argue that Bea might have healed her Pokemon offscreen before her battle with Ash.
2. By your reasoning, we see Riolu spar with Pikachu right before Ash battles Bea. So based off your own words about "Pikachu being the strongest on Ash's team", shouldn't Riolu be all the more tired before its battle with Bea's Grappaloct? Lol. I mean, we don't see Ash healing Riolu. He might have done it offscreen. The same could be said about Bea.
Why do you say that it makes no sense that Riolu > Mega Lucario?
For it being a superior species argument
1. We've seen Ash's Hawlucha (One of his weaker Kalos mons) defeat Astrid's Mega Absol, which was her ace at the time.
2. Ash is a much superior trainer than Korrina.
3. We've seen many of Ash's first stage evolutions beat fully evolved pokemon.
For the, it was owned longer/more experienced argument:
1. Ash has owned Pikachu a lot longer than Lance has owned Gyarados. But why is Lance gyarados much superior to Ash's Pikachu?
You're simply looking at the statement. "How can a newly acquired Baby Riolu be stronger than a Mega Lucario Owned for a long time". If you look at just the statement, then yes, I personally would also agree with you that Riolu cannot be stronger than Mega Lucario. But if you look at the actual facts and events that have happened so far, one can easily argue Ash's Riolu is > Korrina's Mega Lucario.
There only reasonable argument here would to be say that Korrina was much weaker against Bea and after her loss, trained very hard to battle Ash. Hence, the Mega Lucario she used against Bea was a lot weaker than the one she used against Ash. "There is no definitive prove of this. It would be an assumption". However, with this assumption, you can argue why Mega Lucario is superior to Ash's Riolu. Other than that, if you look at the actual facts, Ash's Riolu is stronger.