Really, this blows my fucking mind just thinking about it this way. I mean growing up, most would've thought Nintendo would just do this:
Game Boy/Game Boy Color = Portable NES
Game Boy Advance = Portable SNES
Nintendo DS = Portable N64
Nintendo 3DS = Portable GameCube
Nintendo Switch = Portable Wii
It's weird, GBA and even more DS were under their console counterparts, but then 3DS with its modern shaders felt like it leaped to near PS360 territory (but worse than GC in other ways) with games like Super Street Fighter IV: 3D Edition (and even more so with Monster Hunter Stories, thank you Capcom).
Now Switch basically went into MAXIMUM OVERDRIVE and is basically near PS4 and XBO? Beyond PS360 and even Wii U? What kind of voodoo is this?
Your post brings up an interesting point in that the games Nintendo's portable systems have usually received make us equate them to home consoles from past gens in power, despite that usually not being the case.
The original GB paled in comparison the NES (compare SML to the original SMB) in terms of resolution, sound, and lack of color (the GBC would eventually do better with color than the NES could though), but its software was optimized to the point of seeming like a portable NES. Cheaper memory in the late 90s helped as well, and I would put the best looking GBC games (Shantae and Star Ocean: Blue Sphere) ahead of anything on NES that isn't Kirby's Adventure personally.
The GBA was able to accomplish more than the SNES could, yet once again resolution and sound kept it from shining in a way that made it seem worse. I really doubt something like Driv3r would have been possible on SNES, yet the dark screen of the GBA, horrible sound, and less buttons makes SNES ports seem choppy and make the hardware seem underpowered. I'd put it between the SNES and PS1.
The DS is definitely worse than the N64, but there are some nice looking games on the system. Add texture filtering to SM64DS and I'd say it's aesthetically better than the original, but it is definitely running on less impressive hardware. I'd put it between PS1 and N64.
The 3DS is about as capable as a PS2 in my opinion, as I'd average out the PSP geometry with the shaders you mentioned. However, I feel like since portable gaming is less lucrative than mobile and has a much higher development cost than it once did, less effort is put into making these games look nice nowadays, and as a result we kind of have a lot of games that look like cheap mobile games on a very low resolution screen.
You have to keep in mind though that throughout all of these, Nintendo had taken a different approach to portable gaming than its rivals did. The GB launched next to the Game Gear, which was pretty much a portable SMS. The TurboExpress was released when its home console form was still relevant, and the GBA was underpowered compared to the N-Gage. The PSP was around the Dreamcast's level, and I'd say the Vita is the Wii with modern shaders/lighting.
Nintendo stuck with a low price/gimmick selling point for its handhelds that has usually worked to undermine the competition, but mobile has shaken up this model to the point where they've decided to consolidate both of their platforms in a continuation of the legacies of their past competitors. A slightly better Wii U with a modern feature set is what the Vita 2 would have been, and Nintendo has taken this, slapped on a dock and decided to call it their next home console because they know that a portable only console is no longer viable on a scale that it once was.
