The right hand has the harder part. This isn’t apparent at beginner or even possibly intermediate levels, but when you get to advanced, what the right hand does is harder.
With fingerpicking (using individual fingers to strike individual strings) it’s pretty obvious that the right hand job isn’t easy. I’m not bad at fingerpicking, but I find it even harder to play picking patterns with a pick (plectrum). For an example, think of the guitar riff on “Sweet Home Alabama” which is a pretty easy one and I can even nearly pull it off. But even strumming can be a lot more dynamic and subtle than you might think.
I’m primarily a keyboard player; I second on guitar. One time I was in a band and we were playing a Santana song. The guitarist asked if I could play the apparently simple rhythm guitar part so he could play percussion. Sure! Only, when I tried it, even though I got the right chords and timing, the part just fell flat. There was something explosive and dynamic about how he was strumming the guitar and I just couldn’t do it!
Furthermore, the right hand does a wide variety of techniques including resting the heel on the strings at the bridge, not to mention free strokes versus rest strokes, and how much harder those are to get sounding clear than it looks.
As lisiate says, the right hand does a lot of fairly subtle stuff that dramatically affects the tone. A great player can get surprisingly good tone out of a poor instrument.
IMHO, guitar is just plain harder than keyboards, because it’s a lot more subtle. In addition, you need very precise coordination between two hands doing very different things
As Bach said, pianos are great: you press the key, and the instrument plays itself. Of course, a good keyboard player takes advantage of this ease to concentrate his or her skill on other areas. But I do think it’s easier to be “half decent” on keys than on either electric or acoustic guitar.
Regardless, I’d recommend a lefty learn to play on a righty guitar. Regardless of which way you start, you should be able to do well with enough practice. It’s easier to find good (especially used) gear, and you can play someone else’s guitar (in a pinch or for the fun of it). Ditto golf: there’s even less point in learning to play golf left-handed. Fencing or tennis is the opposite: learn lefty if you possibly can!