Why is NRF a requirement for this?
Other than that, both the percentages and days are way too big, and the ROI seems to be very low depending on which nation you colonize. If I were to choose to colonize someone with 25m daily revenue, I’ll already have a quarter of my investment back in 5 days. I can just abuse this as a raider over several nations, repeatedly.
Think of it in a full scale war scenario, where someone decides to take half of your revenue for 5 days, in addition to doing infra damage on all of your cities and looting your war chest already, while also being in at least 2-3 different wars. This is simply crushing the losing side even more.