I opened it up in Brawlbox .67b, because I noticed that the angle that Sonic's dair sends at is definitely not outside the meteor angle range. The range in brawl is really wide.
I found this:
View attachment 216
363 is one of the the autolink angles.
And you can only meteor cancel a move if the move's actual trajectory is within the meteor range. If you set a move to have an angle of -90 you won't be able to meteor cancel it.
Simple solution:
change the angle to 290.
tested it in vbrawl and the angle seems good.
so, yeah.
Then, everything should be fine. And we can stop this Sonic dair flame war that seems to have been going on for years.