In the US the pricing is as follows (assuming you're not a student and just a single person):
Apple Music: 109 USD / year
Apple Arcade: 49.99 USD / year
Apple One is 16.95 USD / month, which means 203.40 USD / year and additionally comes with Apple TV+ and iCloud+.
Answer: It is not cheaper to get Apple One. The two individual services you're using and paying annually for cost you only 158.99 USD every year, while the Apple One plan would mean you need to spend an additional 44.41 USD every year.