Okay, for my Lucas, when the opponent is at 80 I can usually fish around for the Dtilt lock, especially as Dair is one of Lucas' safer moves. If it's not working, you have to go to other tactics. You get an almost guaranteed kill at 150% with most chars using Dthrow (I think the strongest in the game from memory) and magnet gets lethal around that time as well, considering the angle at which you send your opponent.
Lucas is one of those characters where being on guard can make most MUs a billion times easier. Keep on the watch for energy-based attacks, for instance, and you'll save yourself a lot of damage whilst making the MU far better for yourself.
His headbutt I think kills most everyone at like 170 or 180% and his Fair starts murdering at like 200. You know most of this, i'm sure, so i'll get to the important part.
Lucas is one character where the opponent does not want to mess up against, ever. All his smashes are ridiculous and even his Fsmash can kill at like 120 with ease. If you feel out-ranged, play bait and punish. Getting camped: Moved to a platform, magnet or mix up your approaches. Ftilt is an amazing gtho move, as you noticed.
I dunno, your Lucas is pretty darn good, IMO. You need someone better than me to really comment on how your individual Lucas could get better. :o