The person I quoted was speaking of "raw power" not how much the actual real world performance is visible. I shared the link as a simple guide. I don't have the time to provide many different source and a tech argument to somebody who obviously hasn't looked deeply into it. The link I provided was actually pretty conservative in its estimate as well. 

As for marginal benefits/margin power we must consider the law of diminishing returns. 

In terms of raw power, yes, the 3DS outperforms the PSP. Just like the GC outperformed the PS2. Neither difference is huge - as in a generation huge, but they still exist. 

If we want to also talk about feature-sets of course, the 3DS has a more advanced GPU with many advanced shading and lighting methods that the PSP did not have. The one advantage the PSP has over the 3DS is pixel density, and that can be a significant enough advantage in some games, while not so significant in others. Sure the games you listed wouldn't look out of place on the PS2, but neither would FFXII, SoTC, and GoW look out of place on the Gamecube. 

Presuming Nintendo's next handheld actually will outspec it. There's certainly a possibility that it won't.

How does the PSP hold a pixel density advantage over the 3DS? The PSP is 480x272 which is PPI of 130 whereas all variations as far as I can tell of the 3DS are higher ( on the top screen at least)  Correct me if I'm wrong on this part however, as I'm only going off what I've read on websites.

Also, no one was stating that the 3DS isn't more powerful, we were stating that games across the two devices look very similar (which they do).  All I was stating was that in real world terms, there was very little difference between one machine from 2004 and one from 2011, which demonstrates how powerful the PSP was when released.

On topic, the Vita is the same as the PSP, it got a hell of a lot of power in there so in theory it "should" last for years.  But with so much of the console left untapped apart from 2 or 3 launch titles, the whole machine is going to waste.

The 3DS's PPI ranges from 86 - 124 depending on the SKU. We are using a resolution of 400 x 240 not 800 x 240 (in 3D mode) because you don't see an improvement in pixel density in 3D, in fact aliasing is more noticeable. 

He said, "raw power" not "observable differences." I agree, the observable differences between the 3DS and PSP aren't huge, but all the next Nintendo handheld has to do is be a little more powerful than the Vita, and it can take third party developers (assuming a large userbase as well.) In fact, if it were vastly more powerful it could hurt the next Nintendo's handheld's chances with niche developers because development costs would rise as well. 

There is a possibility, but it's relatively small.

1. The Vita is comparable to three year old phones in terms of hardware. You can find phones with Vita level hardware for $70. That is how quickly the mobile/handheld hardware is changing.

2. Nintendo is planning a unified platform with "cross-platform" games. If they make their next handheld too weak, then this would be difficult to develop and plan for, assuming their console form-factor is at least a little bit more powerful than the Wii U (and we should assume it is a little bit more powerful than the PS4/XBO at the least.) 

Nintendo wants to do both. 

"Iwata specifically called out the difficulty of porting a Wii game to 3DS, saying it would require a "huge amount of effort" because the software architecture is "entirely different." The same issue crops up when Nintendo tried to port 3DS games to Wii U, he said."

"Nintendo won't face these issues going forward beyond the Wii U and 3DS, Iwata said, because the company's new unified approach will allow consoles and handhelds to become "like brothers in a family of systems.""

Those quotes there are litterally just what I said.

There is a possibility, but it's relatively small.

1. The Vita is comparable to three year old phones in terms of hardware. You can find phones with Vita level hardware for $70. That is how quickly the mobile/handheld hardware is changing.

2. Nintendo is planning a unified platform with "cross-platform" games. If they make their next handheld too weak, then this would be difficult to develop and plan for, assuming their console form-factor is at least a little bit more powerful than the Wii U (and we should assume it is a little bit more powerful than the PS4/XBO at the least.)