You need to know the difference between the two first: Style is a manner of doing or presenting things. Fashion is a popular aesthetic expression at a certain time and context.
Basically, style is how you present yourself. It's individual while fashion is what's popping at the moment. It isn't necessarily tied to clothing. An example, remember the dab? You could say that the dance move was fashionable at the time until people had their fill. Are you dabbing now as much as you were then?
That's a good representation of why style is better. Fashion changes really quickly. It barely lasts a season until everyone else moves on to the next thing. Before you know it, you're the only one in the crowd that's still doing the same dance move, wearing the same clothes or having the same hairstyle for years.
With style it's individual. You can dress however you want in a way that appeases you. If it's genuine and true to you in good taste. It's going to be noticed and appreciated. Style is timeless it doesn't matter whether 10 months or 10 years go by. Your dressing for yourself and not for the general public.
With fashion, multiple people could have the same thing so you never really stand out. Your just one among millions. That doesn't necessarily mean you look bad. It just means you wouldn't stand out. If your the type of person that wants to be noticed for how you dress. Don't focus solely on what's hot, everyone else will definitely have it. Focus on what speaks to you. Sure you can try out some fashionable items it won't hurt. Besides, it's fun to compare and be part of the crowd every now and then. Plus you never know, what's fashionable might end up becoming a classic.
Oh, keep in mind while your out buying the hottest thing in the market every season, your pockets are getting thinner. Fashion is expensive! What did you think, all these brands were giving them out for free? Unless your an ambassador of the brand, a celebrity who gets paid to promote them or resell the garments you just bought for a profit. You're pretty much making a loss. On top of that, purchasing and storing all the clothes you have in bulk isn't really environmentally friendly in the long run. In the end, it's all based on your choice. You could or could not be fashionable or stylish.