It really does depend on your time frame, does it not?

This is part of a 2 year, €13 billion investment by Google, so €5 billion is nearly all of the yearly investment of a single project.

On the other hand, Finland is only a part of Google's world-wide projects, and these projects are expected to produce revenue for, what, decades?

A 10-year time frame changes your numbers to ~0.1% and ~0.2%.