If you pay for office, you should get Office... that pretty much sums it up for me. And perhaps everyone who uses Office won't use Android as their primary content creation device... but I might be wrong.
The benefit of subscriptions is that they typically are more generous with allowing you to use their services on multiple devices (perhaps not simultaneously).
I would say it's similar to saying "I bought Star Wars on VHS, therefor I should get he HD version for free"
The Microsoft ecosystem is much more powerful, and works both online and offline, and it's cross-platform (Windows, Android, iOS), but you don't think any of this is worth paying for?
Perhaps you have much more important things to spend your money on. How much is your smartphone costing you? How much do you spend on Spotify, or Starbucks?
How much would you have to pay Google for the 50GB mailbox and 1TB of storage bundled with Office 365?