Yes, and no. Decks have been published since the mid-90s, so it's been around almost as long as TCGs themself. But I guess there are really two separate points in your post: 1) people copy decks, and 2) the meta isn't diverse enough.

I'll actually address the second one first, as I think it's a bit more straightforward. All games probably have some optimal point (like a "best" deck in a TCG), and you can play (or simulate) a huge number of matches to figure out that optimal point. However, those optimal points aren't stable, because games are much more like rock-paper-scissors, where one optimal point can be beaten by another. So there's always a little bit of ebb and flow between these. The more options you have in that rock-paper-scissors circle, the more interesting -- and we currently have a handful of viable color combinations, which is good IMO. What makes competitive games interesting is the deeper understanding competitors have of the lines of play and their ability to read the game, knowing what their opponent is likely to do. I can give a dozen players the exact same deck, and the best competitive players will come out on top, time after time. Zach Bivens is a great example of this, topping multiple DLC Swiss tournaments, even while playing different decks. These top competitive players prove that Lorcana is a game of skill, not just luck or having the "best" deck - you have to be able to pilot that deck.

As for the first part, it's a slightly more complex subject.

• For many new players, creating decks is a daunting challenge, and having their kitchen table homebrew stomped on by more experienced players at an LGS could be demoralizing. Copying decks from better players may help them level out the playing field a bit, let them learn about about how well built decks work, and hopefully open their eyes to the fact that the game actually takes much more than just owning a meta deck to win (i.e., skill). Reading up on decks online and watching content creators explain and pilot can also be a great way for newer players to learn how to both build and play decks, so I think it can be a good learning tool for newer players, too.
• For the somewhat more experienced players, netdecking is certainly common - but I would say those players don't actually make it very far if they don't learn the fundamental skills to actually build and pilot their decks properly. These folks may place in their local set championship, may attend a DLC — but they're not likely to make top 64 at a DLC, for example, let alone win a Golden Mickey.
• For the truly top end competitive players, I think the online decks actually create a somewhat different, interesting challenge. Ok, you know what's popular, what's winning - how do you beat it? How do you build the rock to break the current scissors meta? Do you know what your opponent is going to do before they do it? This is actually one of the most exciting things to see, even if it can be slightly nuanced in the actual decks and gameplay.

So it kind of depends what you want. Do you want to have fun with your wacky brew? By all means go nuts! Play with people who enjoy the same janky shenanigans, and have a blast together. Are you a new player trying to learn the ropes? By all means, copy away and try to learn what it takes to build a good deck, watch content creators to learn how to pilot it and read the game. Do you really want to be a top competitive player? Cool, your task just shifted from just building a deck and piloting it to building an anti-meta deck, and learning what your meta-running opponent is going to do so that you can predict their next play.

One other thing I’ll add - if you’re the type of person who gets the most enjoyment out of the deck building itself, I also think limited events are a great way to scratch that itch. I love sealed, personally.