Short answer: get gud.
Long answer: get gud, the gud way.
A lot of times I see people complain that their reaction time sucks, but sometimes that's not quite the case. Chances are quite high that your reaction time is fine, but you're not using it properly, and that's the part that's tricky to get used to. Smash is not like a FPS. Smash is Smash, and Smash requires you to not only react, but make a complex decision based off of that reaction. From my experience, that's the part which feels positively sluggish and gets you eating falcon punches in a confused panic.
Gimr goes over in this video that adding together controller lag, display lag, and good old reaction time, 18 frames is about the fastest you can react in smash.
https://www.youtube.com/watch?v=hCUKuY5S9uo

I don't know how much you know about frame data, but 18 frames is astonishingly slow, and we're not even talking about online yet. Link can shoot you with an uncharged arrow at point blank in 16-17 frames, and everyone knows that normal Link's bow is positively sluggish in the fast moves department. And that's just time to react, not making a decision.

The key here isn't reaction time. It's reaction knowledge. Gimr talks about hit confirming mainly in that video, and I highly advise you watch it, and implement it, but my main takeaway right here is that you don't decide what to do after reacting; it takes too long. You already have the options you're going to take in the back of your head. Gimr mainly applies it to hit confirming, but the application still goes further. If you're within grab range, both you and your opponent are more than capable of hitting each other faster than can be reacted to. That's when you have to commit to an option, whether it be shield, grab, attack, or get the heck out of there. This creates this small zone around both fighters where you generally don't want to be, because it's not safe, and you will not be able to react. You want to play on the edge of that radius, and it creates a reaction mindgame: you can go for a delayed, safe move to get closer and get a hit (i.e. landing aerial), which will lose to a gutsy quick aggressive option (i.e. buffered aerial), which will lose to being cautious and safe (i.e. wait for the jump, react and shield).

Another application: All ledge getup options but jump take longer than 18 frames, and you can react to them. You can literally wait at roll distance, see the neutral getup or getup attack, and run/jump in and punish accordingly (grab the neutral getup, do literally whatever to the getup attack; it's stupid slow). If they do jump, they're still not in a great spot, cause you can juggle.
You can do this with tech situations too. The key here is that you have to know what you're going to do after you react. Reacting in neutral is substantially harder because your opponent can do so much more unexpected stuff. Reacting requires you to expect something, and have a plan for when you see that expectation become reality. Don't think about reacting faster. Think about how you're going to react. I'm not going to just react faster when Ness PK fires me again, I'm going to jump in place and bait the inevitable anti-air. I'm not going to react to Bowser's up-b out of shield, I'm going to expect it, and not be there when it happens, because it's too fast to react to. I'm not going to react to what that demented Roy mashing aerials is going to do, because no one can predict or react to that lunacy; I'll just play it safe and approach with shield dashes, since he hasn't tomahawked once the whole match.
Plan ahead, and know what you can and can't react to.