By losing Rain, we have just nerfed countless perfectly non-broken Rain users for the sake of 3 abusers (Toxicroak, Azumarill, Feraligatr, Gyarados, Starmie, Jirachi, Tentacruel, Tornadus, Kingdra, just to name a few).
Whilst you did have a solid argument, the facts you used to back your arguement are very very shaky...
Toxicroak is on the cusp of OU, azumarill, feraligatr and kingdra are not OU, starmie will almost certainly be OU without drizzle thanks to its important niche.
Jirachi will most certainly remain OU, and the ironic thing is she will simply be LESS common then she is now.. hardly a bad thing considering she is consistently top 15.
Only Gyarados, Tentacruel and Tornadus are left as OU viable pokemon you mentioned due to rain (and Gyarados could potentially remain OU). We can also argue for what its worth that Tentacruel does have rapid spin and may be relegated to the cusp of OU as toxicroak is now.
Now, lets take a peak at all the pokemon waiting at the top of UU, so close to being viable in OU, somewhat (or obviously) restricted by rain...
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Darmanitan <- major stab is nerfed in rain, protect on 2 major rain threats, easily checked by every rain team
-Chandelure <- major stab is nerfed in rain, fails to drop pokemon like tentacruel
-Heracross (can't take boosted scalds/water attacks, tentacruel walls etc)
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Mienshao (can only be so useful in a meta where protect politoed and tentacruel, Dry skin toxicroak fear nothing, boosted scalds) <- does not threaten rain teams
-Victini <-struggles to make an impact in rain
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Mew (without rain, fighting types increase, and hence their counters)
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Machamp (hates rain teams as they have MANY answers)
edit: bolded former "OU" pokemon (in OU for more than a "few" months) that have been knocked out of OU due to the popularity of rain
Keep in mind before the surge in popularity of rain well after the initial Kingdra + Poli nerf, pokemon such as Conkeldurr, Reuniclus, Machamp, Mienshao were part of the group of pokemon defining OU, Gliscor is slipping of the usage stats as now Terrakion is checked by Landorus-T (which the aforementioned fight types beat much more easily than Gliscor), we are witnessing metagross and infernape's fall from grace. ETC