Two main points
As you said, it's possible to get to 1st dan in three years. This makes the end of your basic training; you know most techniques and can perform them competently. From 2nd dan on there is more concentration on developing the use of theses techniques.
We do practice defending against a left punch and a variety of other situations (grabs, shoves, kicks etc.) The majority of moves start from a right punch, but this is just a general version of 'he's trying to hit me' and training against other attacks is present
The Left handed throws on 2nd dan are reversing the throw (actually starting from a right punch) and learning to do it on the opposite side to add versatile and refine technique. While I agree introducing this concept earlier would be a good idea, it is a minor not a major failing in a self-defense not competitive oriented art, where you want to use the simplest version. Introducing earlier would make them easier to learn an part of the argument for introducing it earlier would be to benefit left handers, while it adds techniques to your repertoire it is not essential.
One flailing of the training is that you can, to a point, make things easy for your partner, but if you want to train hard when you have learnt the move the you can, i have had numerous bruises from speeding up techniques before i got them right and more form speeding up when my partner had. (see my sig)
I say to a point because in the high grading esp the dan grading you a made to go hard & try & hit your partner when the uke & required to block properly & throw hard when you are demonstrating.
My reason for posting on this thread initialy was just ot provide a counter point to a limited bad impression of one club which differed from my expeiance. As i said i there is a wide variation between clubs and i would say look at the individual one.
oh just read the pit aobut the multiple membership things & yes they are a money spinner, i disagree with some of the buisnes practises but this dose neo mean the tequniques are not sound