One can argue about that now. Purely ecologically and economically, every storage system is oversized. Rule of thumbs are just rule of thumbs... But they indicate that one should take half or better only one third of the kWp as kWh. Because only then does the storage really have a chance to be sufficiently charged throughout the year. (You can calculate it, so it is not "made up".) The second rule of thumb is: Not bigger than what you consume in a summer night. Because only then will the storage be emptied often enough throughout the year. So for most people about 200 watts times 10 hours.
If you keep both in mind, with a bit of luck, you can currently even break even (and with the relatively inexpensive BYD). So both rules are purely economic considerations.
If you want more autonomy (for whatever reason that should be good, as long as you are under 100%), you obviously need a bigger storage. But then economics no longer matter, that is then "for the good feeling". Hobby.