If you want to improve playing against bots, it doesn't matter if your playing strength is high enough, but it's best to play against bots rated 2500 or higher. Always play to win. You don't have to have a realistic mindset when playing against bots; the important thing is to play to win and learn from each match. Realistic goals are important, but sometimes a realistic mindset is an obstacle. Training against bots rated lower than 2500 is not recommended. Bots rated lower than 2500 are used to measure your current level and which bots you can beat (they're only good for that), but they're not a reflection of your rating either.
Realistic goals are fine, but when training, you should shift your perspective to what it takes to truly improve.
In training matches against bots, you should play against strong bots and avoid weak bots (even if they're stronger than you). Weak bots are rated below 2500 or, more demandingly, below 2600.
When playing against bots, make sure you have at least a couple of hours free to play a game. Try to calculate as many moves as possible to better understand the games you play. This way, you'll ensure you'll really improve playing against bots. Play with a winning mentality, as if you were a GM trapped in a body with a weaker brain, but with the intention of demonstrating your hidden skill.
It's true that it's unrealistic to think you're a GM, but you have to trick yourself into thinking you're a GM, to motivate yourself and put in more effort when training. Playing against weak bots below 2500 won't teach you much, no matter how superior they are to you. You learn much more with a 2200 human opponent than against a 2400 bot, and the difference is impossible to measure.
If you're able to beat 2500 bots, it might be worth playing against 2200 bots that have an attacking style of play. This way, you can practice against attacks that are easier to counter, but it's always much more advisable to train against 2500 bots or higher. While any bot is fine for fun, it's a different story for training.
For some reason, I beat 1600 ELO bots, but I somehow can't beat a 400 ELO.
I don't know why this is even happening in the first place, and this is why it seems like I'm a 400. What do you guys think I should do? This is probably because of time trouble.
Me against a 400 ELO Player:
https://www.chess.com/analysis/game/live/105006448040?tab=review
Proof I can beat 1600 ELO Bots:
https://www.chess.com/analysis/game/computer/125778797?tab=review
https://www.chess.com/analysis/game/computer/271761896?tab=review