You are not being unreasonable in that the first term is way to early.
I am a student landlord and over the past ten years the date students have been looking or accommodation has moved from late January to November in my city. This is despite the Uni running a campaign for students urging them to wait until the second semester before signing up for a house as there are plenty available.
I think it is a combination of factors driving it though. There is a big discrepancy in the standard of houses available and second year students who may have ended up in a house they aren't happy with are determined to find a better one for their third year, so start looking earlier. This creates a ripple effect and everyone starts looking earlier and earlier.
Some landlords would always jump the gun and start advertising early to get their houses let, which didn't help.
Last year I started getting enquiries in November, I thought this was way too early and also had other obligations to attend to during December, so stuck to my guns and waited until January to start advertising. When previously I would have been swamped with enquiries I got hardly any as most groups had already signed up for a house. When the uni online housing portal opened and I normally would have had 50 phone calls in a day, I had none for three days. All this is a long way of saying, that you can't entirely blame the landlords, it's a two way street.
I would be much happier if letting season happened in the summer term when students are more certain of their plans, even January as it was previously would be better. How to make this happen I don't know as the uni campaigns seem to fall of deaf ears.