This question... Doesn't make a lot of sense. I literally can't understand what information you want out of this.what do you understand under "a sensible test"?
But I digress.
Regarding Lanturn, Lv. 42 is a much more sensible level for Juan since it's close to most of its team, regardless of your choice of how to get to said level and the fact that Swampert is still 10 levels ahead because of your non-standard methods. So let's evaluate its performance.
I take you used Rain Dance + Thunder since you mentioned Rain on Whiscash.
These are fairly good numbers. OHKOs on a fair amount of mons, a reliable damage output against one of the most cheesy bosses in the game, but hits a speedbump against Whiscash, who does put you in a pretty bad mismatch.
Granted, there is a lot of effort involved to get Chinchou up to this level regardless and a large amount of TMs for it to achieve those results, but there *is* a payoff.
Sounds like a C-Tier mon to me. B is not really accurate because of the late availability and Slow Exp. Group making it hard for Chinchou to catch up.
Honestly Xator, I think you're missing the point with your testing methods. This is essentially a tier list for casual runs.
Not absolute scrubs like Little Timmy and his overleveled Starter, but people who know at least the basics.
It's less "deserves" and more "requires" or there's no catching up to begin with. This by itself would create distortions (Like Xator facing Juan with a Lv. 32 Lanturn when in reality no one in their right mind would do so.) but to make things more convoluted, when was the last time you even heard of someone splitting exp by arbitrary numbers instead of per level-up?The idea is that the old Pokemon have so much exp because they weren't sharing it with the new Pokemon so it deserves all the exp for a while to catch up.
It's a concept so unnatural that it borders on uncanny valley. Again, this is a tier list for casual runs. There's only so much thinking one does on a casual run, these games aren't even hard for the most part, and people are pulling out advanced analytics and IV spreads while possibly looking like this:
It may be theoretically fair, but if I have a Lv. 32 Lanturn on my team when I'm about to face Juan, it's either grind time or bench time.
There's absolutely no point in challenging him almost 15 levels behind his ace. Of course the result will be bad.
So in reality, all this does is to prevent the mon from actually having a chance to be tested.