Playtesting, huh? I am completely convinced now. I mean, these citations of being able to tell that infinite turns is longer then 6-7 turns is clearly proof of their brokenness in Rain. And clearly, the high usage of Kingdra means he's broken. Clearly, you can't be implying that with ZERO game mechanic changes for Kabutops, Kingdra, or Ludicolo, that they are suddenly broken simply because the rain lasts longer, could you?
Infinite rain has 2 implications. First is that you don't need to spend 1 turn setting up. That is a MAJOR improvement as said before. Second is that you can no longer out-stall it. Rain teams in gen 4 could still be very difficult to deal with but knowing that they only had 7 turns or so to sweep, you can switch around, sub/protect stall etc until it disappeared. Then they would be at a major disadvantage as they would have to switch back to their rain dancer, rain dance again, and switch again to their sweeper effectively wasting 3 turns to begin another 7 turn sweep. On top of all that, you would most likely have to carry 3 or more rain dancers meaning 3 pokemon with damp rock instead of something more offensively oriented, and 3 pokemon with only 3 moves which makes it that much easier to wall. That is what has changed between then and now.
Meanwhile, I personally made a rain team to test brokenness (possibly the best way to get a feel of whether something is broken or not), and I will tell you right now, while Kabutops, Kingdra and Ludicolo are great sweepers, they aren't broken. Paralysis cripples all three, and the old fashioned Skarm/Bliss core shuts them down pretty easily. Tentacruel hard counters special Ludicolo, Defensive Gyarados counters DDKingdra, Kabutops can't beat Skarmory, Nattorei is a 3HKO from Specs Rain Boosted STAB Hydro Pump. Now, take a look at that statement again, because people misconstrue that very often. The highest powered attack that Kingdra has can't even get a two hit KO. Nattorei can switch in, TWave and cripple a Kingdra before it has the chance to kill, and let's not forget the 80% accuracy on Hydro Miss.
The point you're missing isn't that rain has no counters. It's just they have very few and you often need more than one on the team or you will be swept. You gave separate counters for all 3 of the common rain sweepers. Some of them are wrong too because kabutops destroys skarmory but disregarding that, does that mean that in order to not be swept by rain, I must have nattorei, blissey, skarmory and gyarados on my team?