I still got the romance with Kaidan without the whiskey but this happen if Shepard is faithful to him. Frankly, it only added a couple of lines and isn't necessary at all. You only need to visit him thrice at the hospital so he know you're not a dick. Still, it was more straightforward than choosing Ashley's gift - pick one thing that she'll love the most, everything else will ****** her off. Was gifting women were that complicated? Guys, let her decide what she wants; gift certificates.
Much like her inconsistent character arcs, Liara romance have always been awkwardly done from the start. In ME1, she damsel in distress you rescue and you get her as a reward. In ME2, she was dismissive and her entire arcs was shoved into a DLC. Her character development was expanded in the comics rather than within the game itself. But if you notice it; the talk about how Presidium is beautiful, the talk about mourning her mother, the talk about being busy and working, her coldness and your persistence to make her open up to you; It was a rewrite. Much of her conversations in ME3 was the ones you should have with her in ME1. You're basically restarting a romance with her rather than resuming a romance. That's why it felt off.
For lesser romances, the writers was given a set amount of lines and scenes and they crammed everything inside the allotted minutes and paraphrase the lines as much as they can. There's no chance for them being given a do-over. So, citing lack of time for the only one major romance to a character who they gave the attention the most, is a cop out.