Thought I'd chime in with a few things since I've seen the idea of a built-in battle bot come up a lot.
In the Yu-Gi-Oh community, there are a lot of simulators that do exactly this (EDOPro, and older sims like YGOPro and YGOPercy). These are often used for deck testing after your test hands seem favourable, allowing you to check combos without fumbling in front of a real person and embarrassing yourself. It's a bit different to Pokemon, though, since turns in YGO can take an extremely long time if they're playing something like a combo deck. You could also say it's simpler since these AI tend to follow semi-set combo routes, and have set decks that they'll use, often taken from the top cut decks at national tourneys. However, I really don't know where I'd be without those AI on these simulators, as there are some horrific players you can come up against with awful decks that fold to any sort of meta strategy. These just aren't the right data I would be looking for when going into tournaments that will absolutely be populated with the best decks that I need to know the matchup for, as well as be prepared for. I understand this example can be seen as a false equivalence and isn't directly applicable to PS, but I wanted to give some examples of successful test bots on other simulators anyway.
The bad player issue can be seen on the PS low ladder as well, with the population being worse players by definition that just won't give you the right "stress testing" so to speak. You may see the odd smurf, but that's about it. The teams and players are simply suboptimal: you're not going to be fighting viable teams, nor will you be fighting players who know how to use their teams. In addition, an advanced bot (like david stone's technical machine bot or pre's pkmn.cc projects) could provide amazing insight into prediction, game sense, and how you reveal your team at the right time. I really think a lot of people here are undervaluing the strengths of reliable "stress testing" methods, like, people could really learn from something like this. Hell, you could even use sample teams from various forum threads to fine-tune the AI to the format, this is something the average PS bot can't do. Sure, it wouldn't always be updated, but having something like a custom team feature could alleviate it slightly.
It's definitely an undertaking, but I don't want to see this outright shot down either.
EDIT: One more thing, by battling an in-built bot, you can fight without your teams being seen. This is very helpful for tournament players who don't want to be scouted on the ladder. Imo, there should be an option where you cannot actually have your battles with the bot linked.