Trading is next to no proof of a gen happening at the same time as another. You can also freely trade and battle between Black/White and Black 2/White 2, despite the latter games taking place two years later. Trading is just more of a way to retcon things and is more a game mechanic than a plot point.
The only reason you can freely trade between BW and B2W2 is because they're part of the same generation.
True, that could be said of FRLG and RSE as well, but considering the RSE Pokémon already exist during the time of FRLG, I'd say they're concomitant.
Something else to note about is how Magma and Aqua had no mention in Black/White(despite their actions being far more noteworthy than Rocket) , yet they appeared in Black 2/White 2(as former members of course) and, imo, speak as if what they did wasn't that long ago. That shows that there is also a chance of the big events in RSE happening inbetween both sets of Gen 5 games. That could also explain Steven being champion in HGSS because neither us nor Wallace has probably beaten him yet. I'm sure we also aren't the only silent yet strong trainers around. There's a lot of ways to interpret what we do know. ;)
That's an interesting argument, but RSE can't be after DPP because of all the new moves and evolutions that are in DPP but aren't in RSE. Unless, of course, they remake RSE. I might be inclined to think RSE happens in-between FRLG and HGSS, but never between the two Unova games.
It's pretty obvious that there were more Pokemon that existed outside of those areas. It's not like Kanto was the only region and the others just continuously popped up out of nowhere(we only know of the number of Pokemon as the regions are brought out and because I'm sure they don't have every Pokemon/region planned out already).
With that said, Hoenn and (all) other regions more than likely existed with their Pokemon before we visit them in the games. That, however, does not mean the big events(what we have to go through playing the games) happen together. There is pretty much nothing solid that gives Gen III a specific spot is what I'm saying.
Other than that, the others seem to have a better way to judge where they are.
In GSC the new Johto Pokémon are referred to as "newly found", although FRLG screwed up the logic by introducing Johto Pokémon in the Sevii Islands.
If RSE happened during 5th gen, there would certainly be Pokémon not indigenous to Hoenn that were introduced later in the series, such as Sinnoh and Unova Pokémon. Again, a remake can fix that, but the fact FRLG, which is the very first game chronologically, can trade with RSE without the machine being labeled a "time machine" as it was in GSC, to me may not be conclusive proof, but it points in the direction of FRLG and RSE being simultaneous. If RSE was after FRLG, there would be explicit sayings that it happened after, much like with all Pokémon sequels to date.
Also there are the Orbs in HGSS which allow you to harness the power of the Weather Trio, it's pretty unlikely Mr. Pokémon would be in possession of such items allowing a trainer to summon those Pokémon before Team Magma/Aqua even could. Finally, the Jade Orb, to call Rayquaza, didn't even exist in RSE, it could have been discovered later on.
And remember that in Emerald, which is the true canon for Hoenn (as B2W2 demonstrates), the protagonist does NOT catch any of the Weather Trio during the storyline, making them available for Ethan/Lyra in HGSS.
As I've mentioned before, what do you make of Plasma not making any mention of Magma and Aqua's actions in BW(despite what they were trying to do was a lot more notable than Team Rocket), while former Aqua/Magma members do appear in B2W2 to mention it? That shows that RSE could have taken place between BW and B2W2 as well.
Very slim chance. I haven't played B2W2 but I've seen videos of those NPCs and IMO you're seeing only what you want to see here. BW also makes mention of the Go-Goggles. It was probably just a nod to Hoenn (like pretty much everything Hoenn-related in B2W2).
Sincerely though, I think Cyrus was infinitely more dangerous than Archie/Maxie, so his actions would leave a much bigger impression, enough to be known by Team Plasma. The Team Plasma Grunts also don't make mention of Team Rocket, whose actions are way more "down to earth" and, therefore, more likely to be believed and known by ordinary people.
Before you go on a rampage stating something as WRONG!, please bring up a real argument yourself instead of just saying something along the line of 'this site says so so it's right'. Bulbapedia, while it has an abundance of knowledge, also lacks much solid proof to indicate a specific placement of RSE in the timeline. That part is just pure speculation at this point.
Well I'm pretty sure Bulbapedia put it there for a reason. The reason is that, to date, the place most plausible to fit RSE is during the events of FRLG. There's way more proof of that than there is proof of Hoenn happening between BW and B2W2 (in fact, there's no proof of the latter).