Alrighty, time to put in my 2 cents.
Lucario, as he is now, would likely be the worst character in the game if he could not cancel on shield. Just because you feel overwhelmed the first time you encounter someone good using him, doesn't mean there isn't a way to work around everything. Weaknesses are a lot more noticeable when you actually use the character yourself. He would also probably the unsafest character on shield ever.
As he is now, Lucario has a pretty terrible approach. His air game is hard to follow up because his air physics don't really compliment the trajectory of his attacks. He is pretty limited to staying on the ground in order to really get damage on you. With that said, his only real good approach is dash attack. Couple his limited approach options with him not being able to cancel on shield with unsafe attacks. What do you get? He kind of needs to be able to do cancels to make up for having trouble actually getting to you. His only strength as a character is sticking to you once he gets in.
Instead of looking at what you feel is unfair, look at how to avoid it or just straight up beat it. Jab > sideb is literally only 1 frame faster then just straight up grabbing you, which is going to beat your shield out anyway. If you feel that is really wrecking you, avoid putting yourself in the situation where he can just jab you. Same goes with dash attack > sideb. Dash attack starts up on frame 6 and usually reaches you at about frame 10-14 if he isn't right next to you. If you know that is his only good approach, just scout for it and punish it accordingly. Keep yourself at a distance to bait it out and isn't hard to avoid. Not going to bother mentioning ftilt since its literally slower then just grabbing. There is always a space where it is advantageous to be against certain characters, work to figure out that space.
Now to bring up the disadvantages of jab/dash attack > sideb. If the lucario only focuses on that setup, he is missing out on a lot of other potential options. Lets say the jab actually connects with the opponent, at that point it is usually best to follow it with something like dtilt and then any other possible follow up depending on their DI. Lets assume the lucario isn't blindly mashing out a sideb ASAP after the jab and actually look for a hit confirm. Jab has very little shield stun at all so if there's even the slightly break between the jab and sideb, you can usually escape it. Go ahead and try it yourself, you'd be surprised how many times you can probably roll out of it because the lucario is either not being frame tight or looking for a hitconfirm. This is even worse with lucario's dash attack, because if it actually hits the player and not his shield, he usually won't connect the sideb if they are at higher percents and will just whiff it. If you see the lucario is only focusing on getting that guaranteed grab after the jab, then that makes your job easier because you know what to expect for most of the match and you can space yourself to avoid that situation from happening.
On the note of guaranteed grabs, I recall falco having a guaranteed grab on shield with his laser in brawl. Does that still apply for him in project m?