Would this be a sensible or a stupid thing to do?

I feel for him. For English A Level (many years ago) our group had two teachers who split the books between them. One was absolutely inspired, and the other (also the HoD) was excruciatingly boring.

Caleb will be able to give you a better answer but (just in case you haven't seen it ) there is are some sample answers and marking here which seem to show what they are looking for. I promise I am not over invested in your son but it I had a peek at the syllabus because I was just curious as to what poems they were reading .
Hope I've linked the right bit.

filestore.aqa.org.uk/resources/english/AQA-8702-EX-COMMENTARY.PDF

Well at least he enjoys those. though it is he is less enthused, I think given she seems to be a good teacher I agree with others ( and with your son by the sounds of it) now is probably the time for a bit of pragmatism. If he is really enjoying the texts I am sure it won't put him off studying it beyond GCSE if that is what he wants to do, and her thoroughness is probably setting him up well to be in a position to so, again if he wants to.

Not sure that is helpful, but it sounds like it could be a very great deal worse.
He could be doing bits of The Prelude

Ah - haven't asked you whether it is Eng Lang or Lit - sorry - my mistake. Sorry. so ignore text question if not relevant.

Bertrand - you may not wish to say but which texts is he studying?

^" an English teacher who is providing good feedback regularly is hardworking and conscientious"

Of course. Teachers are.^

OP if you accept from the above that the teacher is hardworking and conscientious and furthermore is experienced enough to be HoD then your best action is not to undermine but trust this teacher's professionalism within the limits of the curriculum as Caleb describes it.

I'm an English HoD and I know that lessons in Y10 this year in my department have become far more dull than in previous years. This is due to the new exams, which are more prescriptive and don't seem to lend themselves to being quite as interesting / flexible as our previous syllabus. I can see a lot of my Y10s losing their English spark this year, which upsets me greatly, so I can see how that combined with a less zazzy teaching style can lead to attitudes like your DS's, OP.

A note is unlikely to help, I'm afraid.

It's really dispiriting. She sounds like she is through but just not inspiring. Like a shepherds pie.

Part of the reason for a boring Y10 might be that they have started to prepare for GCSE. DS is in Y10 too, and is doing lots of sample paper at the school, which is not fun you can see.

I don't think he's lucky to have a thorough teacher who gives proper feedback to progress this year, he would be very unlucky if he didn't

In which case your DCs have been very lucky for you not to realise how lucky they are with regards that. Feedback in English for essays etc must take a lot of time especially when teaching several classes of 30+ so an English teacher who is providing good feedback regularly is hardworking and conscientious

Sounds as though your DS was very lucky last year and is lucky that this year he has a thorough teacher who gives them proper feedback to progress.
I agree that any conversation should be had with the teacher herself but with low expectations of change since that will be her teaching style and it sounds as though she is putting in the effort.

Talk to the teacher. There's no reason to go above her head.

My ds is in y10 too. Last year they were doing Living Texts, which embarrassingly took me until about Easter to realise it was a thing - www.ocr.org.uk/qualifications/other-general-qualifications-living-texts-level-1-2-certificate-j945/ - rather than just what his school's English dept were calling the y9 curriculum, and he seemed to be really enjoying it. This year, English is his most hated subject (for some reason he likes to give me frequent rankings of his subjects). I am a bit disappointed, but there's plenty of other stuff he is enjoying, and there was never any danger of him doing English A level, so it's not a big deal.

Not a helpful post, perhaps, just letting you know you're not alone!

Two things that possibly make English feel worse this year:
If last year had been more average, this year would also seem more average, rather than bad.
They've dropped other subjects they're not so interested in, might mean English is nearer the bottom of their preferences.

Your day = your DS

I think your day is also at the receiving end of the new curriculum and linear style of course. So that's probably not helping.

It's depressing though, isn't it, to tell them that life is boring, get on with it because you just need to pass. I remember several brilliant and inspirational English teacher who not only helped me get great grades, they also made learning a joy and helped encourage a life long love of literature and reading that continues to this day and is the basis for so much learning

HSM

Don't do what I did at DD's parents evening. Told the physics teacher that DD was really enthusiastic about physics last year. He asked if he was not as inspiring as the last teacher ... awkward silence!!!

The priority is getting the best grade possible. This will mean less time on the aspects that make the subject enjoyable. I think this is just part and parcel of year 11. Sending any emails about this would be a terrible idea. If you think your ds is not doing well then contact his teacher to discuss. If he is just saying he preferred last years teacher and enjoyed it more then that comes under the heading of tough luck.

What advice would you be asking for?