You are right in your own way. Tea drinking is a personal enjoyment and there is no right or wrong way. It is good that you can distinguish between few types and scenarios but if you seriously pursue it, your curiosity will increase then all the big fuss start to matter. It is not a bad thing but another form of enjoyment. Cheers!
For Yancha traditionally shui ping is the preferred shape. Shui ping has many shapes but most of them are used traditionally. For me a good shape for Yancha depends on a few considerations:
1. Fast flow - so that I can control the milliseconds
2. Slightly flatter, so that all the tea leaves are immerse in water, I like to fill the whole pot with tea leaves.( the way of arranging tea leaves inside the pot is another big topic, so I will skip this...
3. reasonably but not too big opening for me to control the types of stream of boiling water going into the pot. If too big I will have problem " pressure cooking" the brew. If too small I can't get the right stream of boiling water in properly.
Having said that, sometimes I just abandon all the considerations if the pot is too nice and I just want to enjoy the pot aesthetic rather than being fussy over the shape. It is nice to be wrong sometimes so that you can see clearer from the right point of view.
Normally, I prefer about 100-120ml size pot. You can use this style to brew Puer too or any other tea.
So, it is just traditional way and a fun way to learn the traditional style. Any other styles or preferences are eventually up to anyone. No one is right or wrong. I brew Yancha in mineral water bottle too.