There are tid bits of information you Lucas mains don't give out which make this MU easier.
SDIing the d-air will avoid the jab lock.
SDIing u-smash can save your life if you get hit by it. (It happens. Lylat is an annoying neutral against Lucas.)
Speaking of Lylat and platform stages in general, d-smash is a *****.
Speaking of d-smash, lol at using it as an edge-guard. The Samus can avoid the hitbox with usual planking and then punish the ending lag.
You can buffer shield before Lucas's 3rd jab connects.
You can buffer shield so d-tilt->f-smash NEVER connects.
At low percents, Samus can jab in between Lucas's d-tilt combos.
(The above statements involve good human reaction time obviously.)
PF already mentioned up+b OoS against approaching d-air.
Our d-smash outspaces all of your ground moves, even f-tilt. Don't be stupid.
On the other hand:
Lucas can SDI up the ledge-hop f-air and punish with u-air (I've died to this several times.)
Yes at the above, you can space a f-smash if the Samus chooses to land on stage with f-air.
Running and power shielding works as a legit approach as long as you know when to jump to avoid the grab. From jumping, you can do any aerial and it'll outpriotize dash attack or still be under z-air's hitbox close range.
(Don't air dodge into us as a way to avoid the z-air camping. A smart player (not even Samus exclusive) can punish this in absurd ways.)
F-air/u-air OoS is annoying.
N-air ***** our shield and as long as you FF it, you can power shield the incoming up+b OoS. (Of course, me knowing this will result in me mind gaming a pivot grab, or turn around jab canceling. But it's good to know regardless.)
What PF said about Lucas's recovery sums it up. Be above us when you recover, or you'll have to be lucky if you don't want to get gimped.
Otherwise, Samus can camp and if the player can predict correctly/play smart etc., Lucas can't approach. But, the issue is the times that Lucas does get in, it usually results in triple the damage output of Samus camping.
Both characters won't kill each other until 140%+ if they both DI well and know how to SDI and avoid kill moves/set-ups. I've had matches where we've both lived to 170% with PF. I've also had matches where I've gimped PF at less than 100%, only to lose the lead when he lands a surprise f-tilt near the edge of the stage.
What ends up happening is whoever has the percent lead controls the match. If Samus does, she can continue to camp instead of go for the kill move and ultimately a spaced z-air will result in a gimp against Lucas because of it's horizontal knockback. If Lucas has the percent lead, he can very well run around, power shield and wait to just punish a badly spaced z-air/missile cancel for more damage.
Assuming both players know the ins and outs of each other's characters (and their own), the MU is 55-45 Lucas. Just play smart and you have the tools to win.
(That last section is my opinion. The rest is fact.)