I wouldn't say so. I send my friends money I owe them through Venmo. I make most of my online purchases through PayPal. There's rarely a time where I can substitute one for the other. Although, I don't know the details of the two companies in question.
Fun fact: PayPal owns Venmo. They've tried to keep it quiet because the Venmo brand is much stronger independent from the various screw-ups and annoyances of PayPal.
The big difference: PayPal is for the computer, Venmo is for the smartphone.