1. This is not universally true in my experience. Again I ask, is your driver battling for position or just lapping cars in this state?
Both. I can come back after walking away and push a strengthless Bob back into first by selecting the "don't drive like an old lady" option over and over.
2. Your b-spec driver is an AI driver not a human. He can follow a line more consistently than most humans. Is this what you mean by not realistic?
Poor avoidance of other cars primarily, braking at completely unnecessary times, following the leader instead of taking another lane, and the typical AI stuff where a car suddenly becomes unrecognized in certain positions. Lots of people have been pushed for long distances because the computer doesn't know the car is touching them.
3. This is not true at all. The overtake button will get an aggressive response when used in the correct situations and no response at all otherwise. It is true that they will attempt to overtake other cars when they are pushing without additional prompting from you, but this does not mean the overtake command is useless. It will get them by cars that they otherwise would have stayed behind without it. If you want to see more aggressive overtaking, you are going to need a driver with a hot personality. The differences in overtaking lines can be quite substantial. No, they will never do the sort of kamikaze dive passes we do in golding S licenses, but they will cut in underneath another driver to pass if that's what is needed. Remember, the AI's overtaking abilities are drastically different than a human's.
I've seen some aggressive, opportunistic overtaking done entirely on the computer's volition, and I've seen easy chances missed when I give the command. I've seen enough of both of those cases to convince me that I can't have an effect on him. If my car is approaching a corner with another car that it's closing in on, and I tell him to overtake, you think he would make an attempt to brake a bit later and take the inside line. He doesn't. He simply doesn't when he should and can.
4. Yes, they will drive epically slow if you let them get all the way left. It seems this is designed to discourage running b-spec and walking away. Sure you can still win unattended with the right car, but the design philosophy of b-spec seems to be that it wants you in attendance for the race.
First of all, checking my pulse isn't gameplay, and I'll firmly opine that if that was their intent, it's simply flawed logic. If all it takes to win is not straying too far from the "go" button (and that's all it takes most of the time), then B-Spec is no different from slot car racing.
Secondly, the fact that they included races ranging from 15 minutes all the way to 24 hours and offer no pause option tells me that they expect you to take off and let Bob go it alone. Not to mention the fact that Bob is perfectly capable at zero strength, and he can pit on his own good judgement. Some really confusing design choices...
5. No, they don't take blocking lines. They will also happily slide over in front of a car they just passed to allow that car to catch up with a draft. The AI has 0 defensive capabilities basically.
Yep. The AI will move into my way to follow their line, but not to block me. They will not move out of my way if I'm going much faster than them and have clearly "won" a corner or straight. This does happen in real racing, if you didn't know. What this boils down to is, if you're not in front of them, then you don't exist to them. Big time flaw, and I've yet to see it disproven.
Most of your complaints seem to be about the AI, not the b-spec mode. The AI has problem areas and you are tasked with interfacing with it in this mode. That can be frustrating at times, but you just have to learn to manage around these difficulties. You can either work to set up the car perfectly and push in the appropriate spots or just give them something way faster than the competition. If the latter is how you enjoy b-spec, that is certainly acceptable in my book. It doesn't mean the mode is broken though.
The B spec is almost entirely AI, so the complaints apply to both. I don't enjoy overpowering the other cars, it's just the only way I can get past them. An evenly matched or slightly stronger car will get left in the dust in Bob's hands. B-Spec could be more fun if I had more of an affect on the race, but it's still no comparison to driving by myself, so I think it should be truly optional (Ala GT4), not half of the game. In its current state, I don't think it offers hardly anything for gameplay, as I feel more like a cheerleader than a radioed race coach. It offers as much fun as watching my friend race, except my friend kinda sucks. To me, that's broken.