Historically, yes, Ubuntu has put in the most effort into being the most user-friendly, most easy-to-use distro.

However, I would argue that is not really the case anymore because as other distros (especially Mint and Pop!) have arisen for a user-friendly experience, Canonical has gradually abandoned this over the past few years in favour of being more server focused. Most of the innovation for user-friendly design just isn’t coming from Canonical anymore.

The biggest argument for Ubuntu for beginners is that there are more resources such as tutorials for it - mostly momentum.