But that's the thing isn't it? If you're a whale, you're already going to be pulling 5-stars regularly, and the upgrade mechanic is just going to give you MORE 5-stars. My point is that for someone who doesn't pull that often and lacks 5-stars, the "dream" of upgrading units to 5-stars for free is just that... a dream.
3 to 4 stars isn't too difficult to do for free. 5-star is very difficult for now, but I am sure it will get easier with time.
For now, you have to pull those 5-star units, but you're pretty much guaranteed to pull a few 5* units given enough time.
The cumulative probability of pulling one or more 5* characters within 20 pulls (80 orbs) is about 71%, ignoring the fact that your odds go up a bit if you keep pulling on the same banner (I assume that resets when the banner changes).
The cumulative probability of pulling one or more 5* characters within 30 pulls (120 orbs) is about 84%.
Your initial 17 orbs, the 10 from My Nintendo, your normal and hard Feb mission orbs, and the 90 from the first two difficulties is cumulatively over 120.