But the fact remains that Tales of also didn't do well on either SNES nor GC. The first it has in common with many other new SNES RPG IPs which only exploded after being continued on PS. But all attempts to recreate the success it found on Playstation on other consoles has failed pretty badly. And as has been pointed out numerous times minor spin offs on PSP did a lot better than the main games on DS.
Tales of represents a certain type of JRPG that only really strived on Playstation hardware. FFXIII may have created an umbrella for games like Tales of but that umbrella didn't work back on SNES although DQ and FF were both already almost at their peaks then. That didn't do shit for other RPGs (not by Square). The cheap CD medium on PS on the other hand did. Arc the Lad did close to a million from out of nowhere. Star Ocean and Tales took off, other new IPs like Suikoden succeeded. It's funny that Atlus gained only little numbers with Persona.
I'm not only talking about those and I also give a reason for that growth you're talking about. My point is the rise of the mid-level, close to a million selling RPGs and the Playstation are connected and many fans are still making that connection. As long as they know Tales will also be released for PS they really don't have any reason to switch over to another system, unless they have the money to buy multiple systems (most will buy used and sell again for that). Hence the difficulty of the franchise moving towards Nintendo platforms. It might work if the whole genre could move towards a certain platform but there's really no reason why this should be happening. It certainly didn't work on DS, since as I have pointed out, JRPGs on DS performed more closely to SNES than to PS1/2 (increasingly worse actually), DQ9 being the sole exception.
I'm not really sure we have enough data to say that "mid level" RPGs didn't happen at all until PS1, or that the data we do have even supports that claim. Famistu tracking only seems to go back to late 1994 (though they would on occasion give out older figures), so it's leaving out a huge chunk of SFC's lifespan but here's what I could find for non-DQ/FF RPGs over 200k:
Chrono Trigger (Square) 2,030,000
Seiken Densetsu 2 (Square) 1,500,000
Romancing SaGa 3 (Square) 1,300,000
Romancing SaGa 2 (Square) 1,170,000
Super Mario RPG (Nintendo) 1,089,795
Seiken Densetsu 3 (Square) 647,288
Tactics Ogre (Quest) 503,977
Bahamut Lagoon (Square) 474,680
Fire Emblem: Genealogy of the Holy War (Nintendo) 429,673
RPG Maker 2 (ASCII) 234,923
Tales of Phantasia (Namco) 228,738
Tengai Makyo Zero (Hudson) 200,202
Additionally Saturn managed some decent mid-level RPG hits around the same period (late 1994 to early 1998).
Super Robot Tasien F Complete Chapter (Banpresto) 513,782
Sakura Taisen 2 (Sega) 509,091
Super Robot Tasien F (Banpresto) 464,169
Sakura Taisen (Sega) 359,485
Devil Summoner (Atlus) 355,656
Grandia (ESP) 344,555
Dragon Force (Sega) 272,166
Devil Summoner: Soul Hackers (Atlus) 258,678
Tengai Makyo: The 4th Reveleation (Hudson) 234,932
Lunar: Silver Star Story (Kadokawa) 200,035
And since you brought them up, for some perspective:
[PS] Genso Suikoden (Konami) 167,000
[PS] Genso Suikoden II (Konami) 374,319
[SFC] Star Ocean (Enix) 175,861
[PS] Star Ocean: The Second Story (Enix) 700,458
[PS] Tales of Destiny (Namco) 829,618
[PS] Tales of Phantasia (Namco) 550,393
[PS] Tales of Eternia (Namco) 669,248
[PS] Arc the Lad (SCE) 1,090,000
[PS] Arc the Lad II (SCE) 816,949
[PS] Arc the Lad III (SCE) 379,040
[PS] Persona (Atlus) 391,556
[PS] Persona 2: Innocent Sin (Atlus) 274,798
[PS] Persona 2: Eternal Punishment (Atlus) 200,103