Let's turn a blind eye at how people who farmed multiple 40% Boss damage line familiars (not counting double lines) can now easily 120% boss damage on reboot once they get enough badges?
You can overlook a lot of smaller things like gollux, badges, lab pieces, buff coupons, etc (even though they do add up) but can't with this, because this is arguably a solid 20-50% boss dps increase and when you factor in double lines, IED, it can even be more.
On top of that even people who didn't "exploit" the system and had pre 213 spiders and such get literally double the benefit new players can reasonably get with common from familiars. 1.5 vs 3 lines of drop% is huge especially for someone starting out and only has 1 or maybe 2.
In order to have everyone on a semi level playing field reboot needs reasonably priced red cards, better higher tier drop rates, and the potentials need to be shifted to match people already got. At least then people have a chance of catching up to people who "abused" during the time it was possible.
I use "exploit" and "abuse" in quotes because where people draw the line at bug abuse varies wildly and is pointless to argue about when Nexon doesn't draw the line themselves.
As for non-reboot, with my limited knowledge, isn't it weird to be trading cards without the potentials revealed? The same way I can buy items with certain stats I'd kind of expect the same from familiars.