Obviously it's a symbolic feat as well, but it's still impressive
In the comic "Superboy (1949) #80'', Supergirl travels back in time and challenges Superman when he was called Superboy and was her age. Supergirl proved to be far more powerful than him, winning all the competitions and games they played, including a race where she was so much faster than Superboy that he lost track of her, Kara has arrived so far in front of Superboy that she covered herself in stone as a joke. If a 14-year-old Supergirl is much more powerful than a 14-year-old Superman, then an adult Supergirl should also be much more powerful than an adult Superman.
14-year-old Supergirl was considered as strong as adult Superman, implying that an adult Supergirl would be much stronger than an adult Superman.
In the comic "Action Comics #282", it is mentioned that Supergirl will become more powerful and stronger than Superman in the future, and Superman himself says, "She is mightier than I am."
During the Bronze Age, Supergirl ceased being a teenager as she was in the Silver Age and finally became an adult woman.
In the comic "DC Comics presents #29", Superman is struggling to catch-up to a unconscious Supergirl.
In the comic "Crisis-on-Infinite-Earths #7", after Anti Monitor knocked out Superman, Supergirl beat the crap out of the Anti-Monitor and Supergirl in the process destroyed his armor, armor which Clark at full power can't even dent. This suggests that she has higher atack since Clark attacks can't even dent Anti Monitor's armor.
And after she destroyed like 70% of Anti Monitor, it took 2 Superman and 1 Darkseid, with help from like 20 other heroes working together to defeat to finish the job, after Kara already did like 70% of the job for them.
Obviously it was intentional because every moment has an explanation:
The writers didn't stop to think that Kara isn't the same age as Clark, and that a teenage Kara being as strong as adult Clark would mean that an adult Kara would be much stronger than an adult Clark.
The writers didn't stop to think that an unconscious Supergirl would be much slower than an awake Supergirl, and Superman struggling to catch up with Supergirl would mean that Supergirl is much more powerful than him.
The writers didn't stop to think that Supergirl defeating Anti-Monitor while Superman barely managed to scratch him would mean that Supergirl is much stronger than Superman, since in the end it's Superman who delivers the final blow to Anti-Monitor