What a wonderful excuse to go down memory lane!
Here are the last current-gen usage statistics, from August 2010, the month before BW came out:
https://www.smogon.com/forums/threads/smogon-shoddy-server-statistics-august-2010.78421/
- Jirachi was not as popular as it is today. It had a lot of set variety, but Scarf was the most popular set. I think some Calm Mind variant was the second.
Yep, definitely. Bold Wish Calm Mind was really popular/defining in the semistall metagame of late Platinum/early HGSS (explosion of ScarfTar, lots of Taunt Skarm, Gliscor everywhere, things like that), and eventually shifted to running 280 or even 308 Speed for Lucario (you saw this on Phil's dual screens team for example). Then, post-Mence, Superachi was suddenly EVERYWHERE, with HP Ground to devour Heatran and cut through all the FWG offenses that were popping up.
- Heatran had a lot of set variety, but usually either Scarf or offensive lead.
Scarf was pretty much extinct at this time, but yeah, offensive Tran was everywhere. Shuca SR was THE new Stealth Rocker, though, especially outside of the lead position since it just did so much (and non-lead SR ShucaTran picked up as the perfect partner for lead Machamp). Lead Heatran also started running Specs since Overheat was one of the few moves that actually OHKOed Machamp (which, alongside CB Azelf, led to SashChamp picking up) as well as Occa Metagross, and then Life Orb became an alternative to Specs since it still KOed Champ/Gross and you could more reliably SR with it.
- Scizor was extremely popular and metagame-defining.
Eh, still #2 in usage, but this was more a remnant of LatiMence, as CBzor's time was definitely coming to an end. Some players were trying out Scarf (especially bc of the next Pokemon you mentioned), but it would be a while before that took off, as well as bulky SD.
- Gengar sets were extremely offensive. WoW was not common, even after Pt Hypnosis nerf. Protect + HP Fire was one set used, as an anti-Scizor countermeasure.
MysticGar (Tect HPFire (alongside Magnezone!)) was good but died out once Sub + Pain Split was discovered and Latias was banned (and Scizor started dropping). SubSplit wasn't just its new default, but arguably the scariest Pokemon in the tier for a long time, I can't overemphasize that enough - it was considered pretty much uncounterable. Part of the reason Wish Protect Jirachi became popular was because of this Gar...and that exact Rachi is why Gar now runs Will-o-Wisp so much. I can only recall one, maybe two teams which took advantage of SubSplit Gar's prominence and used Explosion on it to lure its most prominent halfway-decent answer - another relic of the past, Vaporeon...
- I really don't remember Ttar sets, but I don't think anyone was running SR on any set.
This is pretty much on the money - if I can be nitpicky, there were a few players (I believe ENZ0 was one, and there were maybe 2-3 more) who experimented with rocks Tars, but it was pretty much nonexistent. Scarf was on its way down post-LatiMence, and Dragon Dance shot WAY up, both as a DDmence "replacement" and to take advantage of the fact it didn't need to run Babiri Berry + Fire Punch anymore since Scizor was going down.
- Sash Azelf (0 bulk, Naive Fire Blast) was the lead to beat. Colbur gained popularity at the very end of the generation.
And the aforementioned Choice Band! There were also occasional rocks LO sets (Psychic KOed Champ, Fire Blast KOed non-Occa Gross)...but yes, this is accurate. Fun fact: ColburZelf was invented by a YouTube player, CooltrainerAlex. Pride of wifi...
I have to go now but wanted to chime in quickly. I remember this time very fondly (and I think clearly) so I may add more later!