If you strip both characters of their weapons and skills, you'll see that actually Camilla has a BST of 158 and Beruka has a BST of 157 - not enough to matter. The reason why Camilla has lower stats is because her brave axe has lower might than the killer axe (8 vs 11) AND because it imposes a -5 speed on the user. So, if you give Beruka her brave axe you'll see that she has even worse stats - for a neutral beruka, it would be:
HP 46, Atk 37, Spd 18, Def 37, Res 22.
So, you'll see that their BST are actually quite similar (for the record, all meleers with move of 2 that aren't dragons have a BST of 157 or 158).
The reason why Camilla is considered superior is because her stat distribution is much better - Beruka is a physical tank that hits not really hard and that will be doubled by almost everyone. Camilla has far less defense and HP, but her speed means she is actually tankier in most cases - and she isn't as vulnerable to magic damage (which is good, as Linde is quite popular lately). Finally, you don't require the sacrifice of a 5 star character to give her a brave weapon - she already has it.
That doesn't mean that you can't make Beruka work - good skill choices can balance out the deficiences and make for a nice character. For example, her natively huge defense means that with some help she can shine as a brave user, not caring about speed - as long as she doesn't get anywhere near a mage (admittedly -Spd/+Res helps a bit with that, but res 25 is still very poor on a character with Spd 15 including the brave axe)