Seems to me like he's right. Fast-faller =/= Semi Fast-faller. There's a reason we differentiate these fall speeds into categories like this. The combo games aren't the same at all, like chaining UpSmashes into themselves basically can't be done consistently on Lucas.
As for how to play this MU, there are a few things I like to do a lot. Firstly, I like to treat this MU similar to Falco in how I move. WD OoS is phenomenal, and honestly, most Lucas players really start to get aggressive once you go into your shield. You've got fantastic OoS options as Samus, and it isn't hard to get a free UpB OoS on any impatient Lucas player. As for dealing with PKF, Zair is probably the best option. You don't really want to be in the mid-range where Lucas can feel safe wavebouncing/throwing PKF at you constantly. If you do land a zair, you can use it to push Lucas into a corner, which let's you establish firm stage control. Missiles and missiles and missiles and missiles. . . you get the idea. Establish a safe position in terms of your range, and then suffocate.
If you're dumb like me, you like to spot-dodge grabs and then punish. DON'T EVEN TRY THIS AGAINST LUCAS, EVER. The number of active frames on rope snake is absurd, and you're going to get grabbed, which leads to a pretty bad time.
When I'm edge-guarding a Lucas, I like to throw out a lot of homing missiles, because it forces them to usually recover low. At that point, you've got the whole bomb info from Barbie, so you get the idea. I don't necessarily bomb (because I haven't drilled it into my thick skull, yet), but bombing and then positioning yourself for a free uptilt that reaches just below ledge sounds like an amazing option to me. Sure, the rising nair can cover options, but going that deep against Lucas can lead to tether-cancel PSI magnet cheese. Nobody likes tether-cancel PSI magnet cheese.