It is in Rosalina's favor definitely; however, the match-up for Ike is far from impossible.
Although my MU experience against Rosalina is limited only to FG, I did encounter a few that I would consider strong. @
AceStarThe3rd, for instance. It has been at least a month or two since we last fought on there, I think. I'm not sure if you remember me.
Sorry if anything said in the following is a reiteration.
Anyway, as for every character, Rosalina is strongest when Luma is present. Luma is an annoyance, allowing Rosalina to attack from a distance, but many of Ike's attacks are capable of easily sending it off-stage (i.e. F-tilt, F-air, B-air, Quick Draw). After five months since SSB4's release, it is still uncertain, even to the Ike boards, whether or not Ike lost range in many of his attacks from SSBB; we were only able to confirm this range reduction in F-air. Despite this, however, F-air now has faster start-up, swings faster, and most importantly, gains the ability to auto-cancel on short hops via the 1.0.4. update. His B-air also retains this property from SSBB. These allow Ike to space, approach, and retreat more safely. Should Rosalina move in to attack, Ike can cover his landing from a short-hopped F-air by immediately using his quicker attacks, such as Jab and D-tilt. Ike's F-tilt is especially helpful as a pivot due to its decent start-up, power, and range.
Attributes aside, now onto recoveries. Rosalina's recovery, although lacking a hitbox, is better as it launches her far and can be angled; the latter quality can especially throw off Ike's edge-guarding attempts. Ike's recovery has been buffed in SSB4, thanks to the combination of gameplay and mechanics changes. The removal of ledge-hogging vastly improves Quick Draw, which can also now be used together with Aether if Quick Draw connects. Aether's horizontal movement was nerfed slightly but Ike's considerably buffed air speed compensates for that. Like in SSBB, Aether can thwart edge-guarding attempts.
As for combos, Rosalina also wins in this category, though Ike's combo game is not too shabby either. Ike's D-tilt before the update was already fast. Now, it inflicts 1% damage more and becomes his main combo tool along with D-throw and U-throw. Unfortunately for Ike, Rosalina's light weight makes her harder to combo compared to other characters, and Ike himself is susceptible due to his status as a heavy.
For edge-guarding, Ike has Eruption. Ledge snap vulnerability renders characters vulnerable for 1 frame and is useful for Eruption's lingering hitbox, which lasts for I forgot how many frames. However, as I have stated previously, Rosalina does not have to aim for the ledge when recovering.
I don't know too much about the customs metagame, but I heard Ike is supposedly a monster with customs enabled, especially when using them to edge-guard. Rosalina's deadly with them, too, I believe. Sadly, videos of customs Ike is lacking at the moment, so Ike being a so-called "beast" with them remains a bold claim to me.
These are what I can recall from my experiences. The match-up is skewed toward one character but shouldn't be as bad as many perceive it to be. Hence, my ratio is...
60:40. Advantage
^-^