No, it's not the same. A Haki barrier wouldn't do anything in amplifying your elemental attributes. It just makes the substance harder or helps in creating barriers. Meanwhile, your slashes become stronger the stronger your Haki is, more or less the same goes for punches and other hard materials too. But swords are the most lethal of them all.
Akainu haki in combination with magma is going to significantly strengthen his attack power same with kuzan, enel, kizaru, etc
Haki isn't an ability mainly used to make swordsman stronger. It's an ability used an accessible to everyone to make them stronger
There are other weapons, powers, and abilities outside of swords. All of whic get boosted by haki