If it was that simple, surely someone would undercut all the retailers that follow the rules - while also following the rules.

Temu is just deliberately ignoring any rules.

Monopoly

So Temu/Aliexpress fixes the rules not breaks them. OP shouldn't be upset.

How are the rules broken? How does Temu fix then?

We have rules that should prevent companies from selling broken and dangerous crap. Should I not be upset that Temu ignores those rules deliberately and floods the EU with exactly that?