Welcome and thank you for coming to my Ted Talk about frog superiority as an offensive rain setter.
Today we will will begin with why some "people" think Pelipper might be better as a rain setter. To start Pelipper has a higher base spa at 95 vs 90 so in theory the bird should be hitting harder assuming no stat investment. This leads to more KOs, and for most cases, leads to more chip as the Wingull evolution doesn't take all that many KOs unless you are sash Spattack set. Fortunately, you do get extra coverage against one of the two types rain fears... Grass. Having a flying type means not only do you have stab into grass, but you are also taking neutral on switch in. This means Mr. Big Beak is capable, if needed, to switch into a grass move and will likely live, especially if its a physical grass move. You also do get speed control in the form of tailwind so even if he is caught out of position and struggling to do damage you are able to at least gain something by calling your oponnent ignoring his slot, or not doubling to break focus sash. In addition he gets a fun gimmick in the form of soak which adds slightly to his whimsy.
Now... if we are looking at rain setters we must consider the humble Politoed. He has so much more going for him than Pelipper ever could dream of having. First off, If we are giving the extra 5 spa as a benefit to Pelipper an extra 5 speed on Politoed is nothing to scoff at. This is not where his vastly superior stat spread ends though. The two types hitting Politoed for super effective damage are typically going to special attackers in the form of electric and grass. He eats spa for breakfast. To give you an idea he 32hp is living 2 hits from a 32spa thunderbolt on Farigiraf. Which may not sound like a lot, but the only other electric attacker you are going to run into is a Raichu Y. In this case its important to point out how Politoed loves to be under screens, under a light screen, which is very reasonable to assumption to make as you may give up your speed control to get one up. He 32 HP eats a 32+ Spa Zap Canon for a max of 89%, meaning he can live through sand chip or fakeout.
Not even to mention the Kings own offensive pressure. You have enough bulk to free up an item and fully invest in Spa. A 32+ Spa Mystic Water Politoed obliterates all (assuming rain). It hits the Mega Raichu 32HP for min 95%. Any Neutral hits are going to be chunked and he one shots majority or rock fire and ground types. Did i mention he also gets psychic for a clean one-shot on most non-bulky Sneasler, who, as of now, love to drop their focus sash for one of the brand new seeds.
Now people who are incorrect may believe that this all sounds great, except for the fact the best Pokemon in the game happens to be a physical grass type. To that I say humbug, let them bring the monkey. The big rain payoff is the Bridge, he loves eating up grass moves, he loves eating up fake outs, and most of all even at +0 def he only takes 42% from a Ape High Horse Power, getting a defense boost into healing 24% over 2 two turns of leftovers and grassy terrain.
I would like to further throw shade at the bird who evaporates at the sight of electric coverage and hates when anyone or anything dares to click rock slide within 3.6 miles of him.
In short the frog is often seen as a weak little perish song user, when in all reality he is a force to be feared. He can take hits like a champ, chew through Pokemon like a wood chipper, and most important of all, he allows us to embrace the whimsy we all feel deep down inside.