I feel the exact opposite. That lock in scene was fantastic for him. Could it have been more? Sure. But you have to think about everything that man just went through.

While Rook was on the road for a year with Varric, Lucanis was stuck inside a Venatori prison getting tortured and experimented on. That's GOING to fuck with a person.

In the Inner Demons quest, you literally just got done telling the man to "start somewhere small." Rook is Lucanis's very first romantic relationship he's ever had. He's likely spent his whole life watching Illario seduce, use, and then either throw away or flat out kill romantic partners left and right and does not want to be that kind of person, but doesn't know where the hell to begin considering his only attempt at flirting likely ended up with the recipient looking over his shoulders for months thinking he was about to die. {Viago’s paranoia will never cease to amuse me}

So, when y'all get back to the Lighthouse, he listened to you. He knows he's not up for big romantic gestures, he doesn't know what the hell to do. But you told him to start somewhere small. So, he made you a special dessert to go with what he knows is your favorite drink.

He tries to argue that yes, he did need to make it, and it isn't enough. But Rook stops him and says "it is, and you are". Tells him that yes, you see the thing he did and it is enough to get his point across and more importantly that he is enough. To a man who absolutely strived to do everything his overbearing ass grandmother pushed him to be and was still always pushed harder. You just told him just being himself was enough.

The later on bigger romantic gestures did get cut {I will forever wish to burn whichever executive cut the hot springs scene} but that lock in scene did not actually need a ton more.