Explained by hyogurou when he talked about the different level of haki.
Let's just say you have a tree in front of you and you just place your hands on that wall and coat them with normal CoA without applying any force, what would happen? Nothing.
Now same thing but you use adv coa, what would happen? The tree gets destroyed without contact.
Normal CoA requires force to break things, to deal damage.
You are mixing up a lot of different concepts.
There is CoA (invisible), next step is Hardening, next step is Barrier, meaning you literally create a barrier outside of your body with CoA, next step is advanced CoA, meaning the penetrating CoA which is the flowing thing, which Hyo states is vastly superior to the barrier CoA he showed Luffy.
You do not need advanced CoA to protect yourself from DF attacks, never stated, never will.
Barrier in itself also does not hurt whatever you want to hurt, you attack with it, does not change that it can and was used to protect against DF attacks. When Sandersonia blocks Luffy´s attack pre-TS with barrier, a DF attack (since he is DF rubber), it bounces off, but it did not hurt him.
Sentoumaru used barrier Haki to simultaneously protect himself and attack, hence why he did the Sumo motion.
Admirals used barrier to completely repel WB´s shockwave that traveled the entire plaza, but it completely dissipated.
Shanks protected his sword against Akainu´s magma, hence why the magma could not advance through the barrier, and it escapes to the side. (and there is a scene that is ambiguous with Marco, could both be barrier or the force of his attack).
CoA has a property that directly combats DF products, meaning attacks or substances created with DF abilities, hence why you can also attack real body of DF users with it, or it lets you protect yourself from DF attacks if you cover your body with it, and that holds true to any form of CoA, once assuming the level is high enough. Hence why DD thought Law could not cut Vergo, since his Haki is supposedly high level, but he underestimated Law and that´s how it turned out. This does not negate the general possibility though.
To be honest, barrier Haki only makes sense if you want to protect something that is big in size (can be yourself, or something/someone behind you), or used to attack a big opponent.
You are still simply judging ice as a physical entity that needs to get broken physically, but not as a DF product that can dissipate when touched with CoA.