It is true that OEM speakers are really poor. But they need to be due the lack of head units power.
I have done some upgrades and I’m quite happy how it turned around in the end. First I damped doors. That made Oem setup sound lot better. Second try was to replace rear speakers with high frequency (but cheap) JBL speakers (cannot remember the model). This was mistake. There was not enough power in the head unit and upgrade made sound worse. Third phase that really made difference was to install Alpine PWD-X5 in to the trunk. Subwoofer was what it needed and it also gave enough power