Why a helmet with 5 mods says "This item has no space for more mods"?

actually, experienced players would not be overwhelmed, because they are already able to recognize the affixes in 99% of the cases. similar with other mechanics. new/inexperienced players would, and would think "wtf is this supposed to mean" type of things

Exactly! Making them find out and avoid doing what the OP just did.

Just going to point out that without the hybrid mod on that item, the percentage armour roll would have been far less. It's the hybrid roll that makes that helmet not crap.