okay, after watching, I have a few things to say.
Its good that you gave us a vid of someone destroying you, so many people are embarassed, and only show vids of them winning, or losing by a tiny. But the vids of you getting pummled are the ones where its easiest for people to see your flaws, so kudos.
I noticed that not only do you like to approach with dair alot, if your above someone and you wanna get on the ground you'll try to dair through everything. Thats normal for a beginner, and I find myself doing it too much. But the truth is, there are many things that can out space and out prioritize pikas dair, mainly outspace though. So basically try and get around rather than dairing through everything, I'm not really sure what is the best way to get down, but I find when pikas dair alot they get punished somehow. Also the dair as I see it is more of a combo finisher rather than an approach. I will use dair as an approach if I feel all I need to do is get them off the stage or something. But if you watch axe and other mad cute pikas, you'll find they approach with nair. This gives you two options, generally if you hit a nair, alot of times you can combo into another move, usually another nair. Or if you hit their shield and they attempt a shield grab, you can shuffle that nair, and rising up air will usually catch them, and its rare that pikas get punished for a rising u air. And that u air will combo into nair/bair/dair/wtf you want to. Even on peach.
You need to work on you control. Just spend some time practicing each day on your tech skill, get your wavelands and shuffles down really solid. I saw some solid decisions, but because of lack of control over your character, you would **** up spacing, or just overall look sketchy, and sometimes get punished for what was not a bad idea. Control over your character has alot to do with how successfull you are.
You need to control your up b as well. Pika has one of the best recoveries in the game, top 5 IMO. The reason for this is cause up b is so amazing. You need to work on just being able to go where you want, and then work on angles to sweet spot from. Sweet spotting is really good as pika, pika can get punished alot if he doesn't do that. Also, A really good angle for pika is diagonally up and in, then in, it gets you to the stage from the farthest point out, more so than waiting till your low and going up then up and in, but thats good too, don't get me wrong. But yea, basically learn to control your up b really good.
get your jump cancles down, I saw a couple missed grabs that would have been less punishable if you JCed it. A jump cancle is hitting up right before you hit z just incase you didn't know. When you miss a grab like this, there is less time your character is uncontrollable.
Upairs. learn it, love it, use it. especially as pointed out earlier, if someone is behind you, just hit up and the control stick and you'll jump, then hit a, its so good.
Also, when using side b, smash the control stick as you b if you aren't already, it gets you farther, but usually a side b isn't nescesary, I know, when your new you love it, but you'll grow out of it, and only use in when nescesarey, it might take some time though, cause I still use it when unnescesarey, I know it, but I love it.
Keep at it, I really love seeing new pikas. Also, I believe chad is living in Georgia now, so you should find him at a tourney and watch, and talk to about getting better and stuff.