to add another super, or split?
2 super hive is not capable to get honey yield. The hive must be twice as big.
Splitting the hive means that you do not get honey at all. And what you learn about beekeeping? Nothing. Only how to destroy hives ability to bring honey.
If you want new hives, they are easy to make without spoiling the summer's yield.
If a hive has one box full of bees and brood, it takes 6 weeks
that is capable to get good yield, Otherwise it uses food to grow more brood.
Lets look my hive now. My best hive had 7 weeks ago one box full of bees and brood. Today it has 3 langstroths and 3 medium. It has 50 kg honey. If day is sunny, it brings 5 kg more honey a day.
This way, when raspberry blooming is finish, it has 100 kg honey at the end of month.
I have half smaller hives and they have now 2 langstroth boxes brood and medium box half full of honey. All their work goes to feed larvae. It takes couple of weeks that they are able to forage full yield.
If my hives are not big enough to forage at the beginning of July, I join them to be good foraging units.
Otherwise my main yield passes by and I never get it.