Of note (mentioned above), if you boost to level 20 then go online, you'll get matched with other level 20 players, so you can't crap all over lower-level players with your awesome fully upgraded abilities. So boosting is ultimately useless no matter how you slice it.

And there are various difficulty settings for the bots. In the Container City vids, I believe they were on easy difficulty. Normal difficulty is where they are hard to distinguish from regular human players, and Hard is where they act like superhuman players.

agree at 100%

Even if you do boost and unlock all the weapons, remember that they are balanced. If you've heard of Team Fortress 2, think of that - each of the 100+ weapons are supposed to be completely balanced, so no one really cares of you boost to get every weapon - every weapon has a drawback, there's no god weapon, and if you're trying to boost for that, this isn't your game.