Android

today 7000-8000 mAh should be easy, without adding bulk or weight compared to phones 2 years ago

A OnePlus 15 (released just recently) has a 7300mAh battery, so right within your range. I've not seen much complaining about bulk, either.

Plastic - plastic is what I want.

I have an old Moto 5 that's pretty thin with a plastic back wraps around the sides and snaps on. It has a nice texture that's easy to grip. It's a brilliant piece of functional design. If only they'd given it a better screen/processor I'd be using it today.

Hell, what does almost everyone do with these premium glass phones? Put a synthetic cover in it so you can grip it and give it some drop protection.

I think it's Apple Reality Distortion that got the better of people. For a long while, Apple was obsessed with thinner and lighter phones and the world was very loudly ??? at them. Recently, Apple had to admit nobody wants its iPhone Air, so the chase for thin and light is over for the moment.

The cries for bigger batteries on regular phones have been very loud for a while. But if Apple doesn't do it, Android makers are loath to try. Now that light is out, maybe there is some motion in a better direction.

Next, bring back all the ports we used to have, and replaceable batteries. I might die crying of joy.

Apparently not, because many people buy glass back phones that are both thicker and heavier than a good synthetic, Then they add a cover to protect the back, making the phone even bulkier.

The smartphone market is goddam moronic in some aspects IMO. It all started when idiotic reviewers claimed the Galaxy S2 that was superior to the iPhone at the time, didn't have the same "premium" feel of the iPhone. In part because it was lighter!!!
Also the Galaxy was way way more durable, the iPhone cracked if you looked at it wrong. So there is no doubt which phone was made from the better materials as in the more functional ones.
But after that "premium" phones were basically all glass despite all the downsides, like adding thickness and weight, and being way less durable, and also glass being more slippery so risk of dropping it is increased too. Unless of course you use a cover, which then again makes the glass back utterly pointless.
There is simply no way glass is a suitable material for the back of a phone. Except moronic reviewers continue to claim so, and phone makers keep making high end phones almost exclusively with glass back.