Is it really an insult to say that someone is stronger?
It is when there's no foreknowledge of the Pokemon. If there was some actual proof (aside from an expressive personality) that Clay's Palpitoad was stronger than Ash's Palpitoad than no it wouldn't be insulting to say that.
However if (real life example), I was known for being stronger than people who looked stronger than me because they were muscular or bigger, or even has some show of being stronger. Then I go up against someone who is roughly the same body size as me. I would find it insulting if one of my friends said that my opponent looked/was stronger than me.
So I freaking took out the Hulk (marvel comics) in my last match with just my index finger and one arm tied behind my back, and yet when I'm against someone who looks exactly like me (in body size, and shape), suddenly they're stronger just because they are more expressive in their personality. I would definitely take offense to that.
Because to me it only makes me think my friends have no faith in my ability to beat my opponent.
Now that example can't be applied largely to the Palpitoad, since Ash's Palpitoad wasn't even battling Clay's but still, to call out Ash's Palpitoad out like that really was uncalled for.
I would've accepted the following replacements for what Iris said:
1. That Palpitoad looks really strong, and looks like it has far more experience than Ash's Palpitoad (which should be true considering Clay is likely 5 times OLDER than Ash).
2. Ash looks like he has a tough battle. Clay's Palpitoad looks far more aggressive than Ash's Palpitoad (which is true because Ash's Palpitoad doesn't ROAR loudly and smacking its foot on the ground, causing damage to it).
And look at how easily Snivy killed the crap out of Palpitoad. I'm not saying Ash's Palpitoad could take vine whip, leaf blade and leaf storm, but Clay's Palpitoad rarely looked stronger.
Now I suppose I would be fine if Iris said what she said later in the battle. I mean Ash's Palpitoad has never really been dealt a lot 4x damage like Clay's Palpitoad.
But to say what Iris said without actually seeing the Palpitoad in actual battling is what I find insulting.
Because its like the concept of "your bark is worse than your bite" doesn't even cross their minds. For all we know Clay's Palpitoad (aside from knocking out Oshawott) could easily have been one of the weakest Palpitoad in existence.
But just because it acts more aggressively when it comes out of its Poke ball. It was necessary for Iris and Cilan to say that Clay's Palpitoad is stronger than Ash's Palpitoad.
Now maybe Cilan can use his Deus ex machina levels of connoisseur tasting and can easily tell who will win and lose in a match and would be more acceptable for Cilan to say what Iris did (only more connoisseur laced) . Iris however has no ability like that and therefore shouldn't have made that comment.
Now like I said I liked how Ash's Palpitoad was acknowledged since its unlikely we'll ever see it outside of battling BUT I think it could've been handled better.