(you can ignore this meme if you don't want to view it, i just made it for fun lol)
in my opinion, rerolling is a blessing for this game, especially for new players
because some games don't give you the option to reroll, like FGO, meaning you're basically stuck with whatever you get from the start and if RNG doesn't favor you, life is gonna be hard.
like yeah sure, that might be normal in the beginning but, would you want that to stay the same way forever?
Would you prefer your battles to last over 30 turns each time? exaggerated example i know, but obviously you wouldn't since that would be a pain in the ass to deal with every time. if 100% eidolons can make your battles just last 10 to 15 turns instead of 30 turns, I would rather take the route with less turns
most newbies to this game will always get that "roll for a 100% eido" advice or at least 2 core SSRs or something for an element of their choice), because that's the best advice they can get from them, and some old players didn't even get the option to reroll at all, much less at these recent 100% eidolons we are getting because they didn't exist at the time they began playing this game
I didn't reroll either since I placed a lot of effort into my own account before I even discovered what rerolling was, but if I had the option at that time I would have. even more so if 100% eidolons were available at that time, but no they werent lol
and let's face it- kamihime is not a newbie friendly game, some people will probably get turned off from playing this by how much you actually have to grind just to get the good stuff. and newbies won't be able to do this at all, and not for awhile until they can get on the level of ultimates (in terms of advents of course, for raids they can rely on people)
and i know that advent material cost reduction for the shop is coming close, but newbies will still have a hard time with that
But if they had a 100% eido, things will be a bit different. if they played consistently, they might not take awhile before they can do ultimates, and they'll have an easier time trying to catch up with most players because that's just how OP those 100% eidolons are. if they're not willing to spend a shit ton of cash just to roll for one (and they might not even get it) then why not get one for free? That's like the best deal you can have for this game right now and will make your life a lot more easier in future content, and as people said they'll attract a LOT of strong players with a full set of MLB'ed support eidos even at just a low rank. I don't even understand why someone would want to go the hard and slow way now..
I know it's not impossible to become strong in this game without those 100% eidos, but if you were in the beginning of a raid while someone else was using that, there's is NO WAY you can steal MVP from that guy especially if he has a decent grid + team. Having one of those is just a fast way to becoming strong, and why not take it?
tl;dr
100% eidos make life easier for newbies in the beginning, its like riding a racecar compared to a normal car
if you want actual examples on how they make life easier then (these ones are kinda common sense)
-much easier to add high rank players, let alone whales for a shit ton of good support eidos already at the beginning of the game
-you can use that element to clear all kinds of content with ease, especially in the future (except the element you're weak against)
-you won't need to farm any other eido for that element in main spot because 100% eidolons are irreplaceable as main eido