On the most basic level: Weak AI that requires a huge handicap to stand up to a human player. Let's assume Noble is fair for a minute (it isn't... a few of the AI bonuses are potentially gamebreaking)... exactly how strong is a human player who'd win their fair share of Noble games (i.e. one in 7 on default settings)?
That's the AI without handouts.
To compensate for its shortcomings, it's given bonuses it doesn't leverage. Not only doesn't it rush the poor human with starting archers, it refuses to use obvious exploits - like only building semi-obsolete units and upgrading them (AIs receive upgrade discounts on all levels).
I don't know... I'd rather give a weak opponent rook odds and have them play to the best of their ability than giving them queen odds and telling them not to use their queen because that would be unfair.
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About the diplomacy complaints... I think a few of them aren't legitimate. Fundamentalist religious leaders disliking you unless you accept their faith only seems reasonable. 'Just adopt mine and let's be best buds!' somehow seems unlikely to work.
Having relations sour if you turn down requests for aid also seems reasonable. If you can't milk your good friend who happens to be militarily weak you might end up attacking anyway... so I suppose refusing tribute dropped you down to cautious
One thing I'm curious about though... does Tokugawa avoid diplomatic penalties for refusing tribute because technologies aren't available period, or will an AI still demand them and automatically get a mutual diplomatic penalty?
If this is possible, the redding out isn't unequal treatment... and even if it does, the tight-fisted AIs don't tend to be more popular (which would make no sense) so any problem from this is relatively minor compared to the usual handicaps.