Dimple have you even played a piano before? Like a proper piano, not a keyboard?
For four decades
What about the left hand? The Bass notes?
.
You are completely missing the point.
The OP wants to know which acoustic instrument is the easiest to start with and at this moment in time what you do with your left hand doesn't matter.
Within minutes I can show a beginner the very easy notes over an octave on a keyboard but showing the same notes on a guitar will cause confusion.
Within minutes I can get them playing a C chord, Am, F, G, Dm and Em without moving a muscle.
Keeping their hand in exactly the same position they can be playing Look Back in Anger by Oasis in 30 minutes which is what I get them doing.
I would need months to show a beginner how to play those chords on a guitar.
Also as lessons advance with left handed bass runs you are now not thinking about guitarists like Tommy Emmanuelle who also play 2 (sometimes 3) parts at the same time.
You're also not thinking about those piano players (keyboards with weighted keys whatever) who go on stage and because the bass end is being played by a bass they only need their right hand while the left hand touches knobs here & there.
OK, I'm not a 'real' piano player but I've got away with basically one hand for 4 decades playing semi professionally/professionally to audiences.
There seems to be this snobbish attitude that if somebody wants to learn the piano then they must mean they want to know all their scales and playing advanced concertos where most people just want to knock out a tune.