Mostly, yes. It's easier to seek evidence that other names on the leaderboard correspond to real people (especially in the high leagues where there aren't many tournaments going on at once). But seeking evidence that a specific opponent's "replay" is a real replay is much more difficult. We can identify many "replays" that have scores matching their plant selections, but that doesn't prove they are real.

But as is said elsewhere in the thread, the developer has little incentive to actually fake everything, since score recordings are easy and cheap to produce, transmit, and replay, and even with real opponents (and a few bots to fill in when real replays are scarce), it's very easy to control player progress as much or as little as they want to, just through matchmaking logic.

It's not like in Street Fighter where ultimately the players are in control: If the most inept beginner is matched against the greatest expert in a game like that, then the expert might still lose, since the match is real and live and under the players' control. Maybe the expert will have a heart attack during the game or something, for instance. The outcome of the match is never completely under the game developers' control. Matchmaking has a heavy influence on it, but doesn't completely determine it. But in this game, players don't actually interact at all during a match, so the outcome of the match is 100% determined by matchmaking logic.

They already completely control how much or little we win. They could be using bots like you say, but they don't need to do so.