Nah a bunch of units in future fight are extremely strong and trivialise a lot of content, heck they recently added one of the most powerful units to the new player experience, so that new players don't feel left behind on all the content there is to do. One could argue that this would curb spending on paywalled characters, since she's actually better than a lot of them.
But like all gacha devs, netmarble knows the largest part of their revenue comes from the big spenders, giving away a bunch of selectors and resources really isn't going to impact that at all. What it does impact however is the retention of anyone who doesn't fall in the large spender group, but the group that wasn't spending, still aren't going to.
Dokkan's coin system is much faster than 9 months imo because there are plenty of celebrations throughout the year to jack up the stone count; also the 500 coin units aren't completely fair to use as the average because ffbe doesn't have an equivalent to them, and there are also much fewer of them; they'd also require you to basically summon exclusively on those banners. The average coin cost would be 324 coins which, with a celebration thrown in, would be yours in about ~4 months.
UoC on global is 2 per month, but I've honestly missed a couple simply because I either didn't have enough time to grind out 150k points, or didn't have the bonus units to even attempt to get it. Still, missing none that would be 5 months of saving up; this is not the group that affects revenue at all, since like any business, they rely on monthly income, which is what the 'whales' take care of.