I actually think [name_m]Lucas[/name_m] [name_m]Dahl[/name_m] would be very handsome. And even out the flow, while still giving the option to use [name_m]Luke[/name_m].
I definitely prefer [name_m]Luke[/name_m]! [name_m]Lucas[/name_m] is nice, but it’s not a favorite of mine. I just love the sound of [name_m]Luke[/name_m] [name_m]Dahl[/name_m], it’s so distinct! If [name_m]Luke[/name_m] is the name you love, then go for it! It’s a well established name in its own right, it doesn’t need a longer version.