The thing with Lucas is that while he has projectiles, they're all incredibly mediocre, and carry great risk in using them within a certain range due to their noticeable end lag, even PK Fire. I don't find myself using PK Fire much as a zoning tool, much more as a damage racker or offstage finisher, because I feel it's too slow, but I have seen players use jump back PK Fire to great effect. PK Fire is more effective used in the air as you're landing because it pushes you back, putting a bit more distance between you and a speedy character in case it gets blocked or avoided. But I would suggest always using it near or outside of its maximum range to minimize chances of a punish. And as annoying as it may be, if you short-hop spam PK Fire, it can actually be quite useful.
Z-air I prefer over everything. In Brawl, I based a lot of my playstyle from Mekos, who uses Z-air to land laglessly, and in this game I pretty much always land or short hop with Z-air. It's uncancellable and destroys incoming projectiles, has stupid good range, and has negligible landing lag so it isn't punishable. If you get into the habit of using z-air all the time you literally can't be "outzoned", and sometimes I use it as a mixup and empty hop to bait out shields or rolls and punish accordingly. The few ways to get past Lucas z-air spam is to jump over or roll, both of which can be taken advantage of. When you're not jumping with the intention of chasing down your opponent with an attack, try getting used to jumping and using z-air immediately, and again right before landing.
