Just going off Smash Bros Wikia here
Changes from Melee to Brawl
Captain Falcon has been severely nerfed from SSBM to SSBB (one of the biggest nerfs from Melee to Brawl, despite having some good buffs). His attacks are slower and have been given less favorable hitboxes, which makes safe approaches and landing blows difficult. Additionally, his traction is significantly lower, now one of the lowest. Captain Falcon's down aerial now has a sweetspot, smaller hitbox, is weaker, and can no longer Nipple Spike, meaning that he has a harder time meteor smashing in general. The Knee Smash (forward aerial) is much harder to sweet spot and is slightly weaker in terms of knockback (though it is stronger in terms of damage output, if only by 1%). In recovery, his falling speed is lower (but it is still very fast in comparison to other characters in Brawl). The Falcon Dive can now grab edge-hoggers and has a larger grab-zone, making Captain Falcon harder to edgehog. It also travels slightly more distance vertically, but much less horizontal distance; and can break targets in "Target Smash!!" mode. On the downside, Falcon Kick no longer enables him to regain his second jump, and Falcon Dive travels much less horizontal distance. The Falcon Punch can now be reversed for a short time during the startup. The Falcon Punch has less startup time, but lower knockback. Captain Falcon is now able to swing the Home Run Bat like other characters can. Because of this, he can now properly use a Home Run Bat for a Homerun Contest. Captain Falcon's forward smash has been weakened significantly (now has only slightly below-average knockback, compared from being the 3rd most powerful f-smash in Melee). His down smash is weaker in terms of knockback, adding up to his nerfs. Raptor Boost is easier to use and makes a "leapfrog" effect when the attack connects in the air, making it much safer to use in the air. Overall, Falcon is a slower and much weaker character in Brawl. He is no longer the 3rd strongest character, now he`s most likely the 19th most strongest character in Brawl.
You can't blame it all on the engine Smashchu.