I'm just asking if those three consoles had the power to run their own versions of Guitar Hero/Rock Band smoothly...

I don't know, maybe the limited storage of N64's cartridges would have been a problem.

Other fact is that by the time those consoles were out gaming wasn't as expanded as when the first Guitar Hero was released, so I don't know if it would have had the same success...

I dont see why not? Prappa the rappa was a similar game on ps1 and it looked fine for the time. Ram could be limiting for songs notes etc...but im sure they could downsample the song to mp3 format or something.

I think media would have been the biggest hurdle. Playstation seemed to be the best at having "actual music" soundtracks in the game. N64 carts normally used midi files and I don't think would have been able to handle it. I'm not an expert at firmware and development but I speculate that Sega Saturn could have very well had a problem with the Guitar Controller. I seemed to recall there being an issue with periphrial devices not made by SEGA.

So Maybe the PS1. With a much smaller library of songs.

Well you have DDR on PS1. I guess it was possible but devs didn't thought about it.

On PS1 and Saturn, yes, absolutely.

On N64? No way. Unless you want near-MIDI size songs, it wouldn't of been very good.

As stated, you had PaRappa the Rapper and UmJammer Lammy on the PS1 which were rhythm based games.

Ultimately, the evolution of the genre game with the revisions of what made the game(s) good, and not so much the hardware.

That's exactly what I was gonna say.

The PSOne could have handled it. It probably would have looked slightly worse than Guitar Hero DS.