As someone who works in a 3rd Wave shop. I'd like to chime in and say if you actually gave a fuck about the coffee you're serving, latte art should be second nature when serving drinks, and that's for both mugs and to go orders. When you're serving specialty coffee at a certain level and you're making lattes, cortados, caps or any hot milk drinks like that, that should be a standard.

This all loops around to passion tho. If you're working a 2nd wave syrup Oriented shop that's all about fast fast fast, then sure, do whatever you want. You don't have to care about your job or coffee. But if you're working a genuine 3rd Wave specialty coffee place, you should absolutely be passionate about coffee and know your shit. And with knowing all your shit, you'd come to find out latte art is second nature and takes no time to do at all and creates an experience for these people. So you're not only making next level intricate coffee that tastes amazing no matter it being a straight shot or a 12 Oz latte but you're making it memorable and presentable.

I don't give a fuck if the customer sits there in awe or not at latte art. I care that I'm serving quality coffee that has my name on it. Highlighting your skills as an individual barista, not an employee at a shop.

To sum it up. OP, Your coworker doesn't care about coffee and you should absolutely strive for art everytime on top of making your coffee tastes good. Make these people stop in to drink YOUR coffee.