IMO, purpose in life as motivation to live is a double edged sword. It motivates someone for sure, but when he/she lost the very purpose, depression comes, even suicidal thoughts.
Which is why I like the concept of Dukkha in Buddhist, that knowing how meaningless I am can make me enjoy life more and not caring too much unimportant things, such as comparing myself with billionaires.
For me, purpose comes from my impact on other people. Is it positive? Does my existence lower the suffering of others?
I don't think purpose should be comparative.
I'm not very familiar with Buddhism so I appreciate you sharing. For philosophy, I tend to look more at Stoicism. What I take away from Stoicism as it relates to purpose, is that how you live your life is more important than the things you accomplish. Living a virtuous life can be a purpose onto itself.
Which is why I like the concept of Dukkha in Buddhist, that knowing how meaningless I am can make me enjoy life more and not caring too much unimportant things, such as comparing myself with billionaires.