What particular issues have you experienced?

It’s extremely hard to use reliably.

Anyone enthusing about this API hasn’t done much with it.

What exactly hurt the reliability? Early on, I often ran into false starts because I did not pay enough attention to proper render blocking.

It’s a ridiculous API that is way too complex.

Try using it and you'll see.

It takes huge amount of setup which it then seems to pay attention to or not, depending on his knows what factors.

Go ahead try it for something beyond basic usage then tell me how reliable and easy it was.

I tried something here: https://vtbag.dev Took me a while to figure things out, but I'm happy to share what I learned. That's why I asked: I would be glad to help with concrete problems.