Preliminary notes : The grid showed is not optimized (Cosmos staff with only 5 staff is not efficient) and will probably change when the new water M2 weapon gets released.
Otherwise, Romeo 5* feels like an extremely solid unit. His DPS is extremely high, and his nukes actually deal great damage (especially post ougi). You pretty much put him into amplified mode, and forget about it since you never want to switch it back. His EMP support skill + having some crest generator characters allow him to have crests, which regenerates his passive stacks. His debuffs are great, you can very close to capping all the debuffs turn 1 with a Bonito call. His tanking is crazy thanks to his unchallenged effect at the cost of two crests. Having Kolulu helps sustaining the amount of crests, as they run out fast if he gets targeted.
He's also a very good pick for OTK now that he brings 25% total def down with an ougi without any additional click on top of his post nuke damage, which makes him a better Lyria basically.
Basically an ideal character to deal with Wilnas' bullsh*t, as he's pretty much a more offensive version of Lily.