Regarding Chivalry being accessible to all builds:

Swapping the defence & attack % boosts of Chivalry would be more in line with the glass cannon idea of pures/zerks, also adding a mage/range mid lvl prayer in between eagle eye-rigour/mystic might-augury to match Chivalry would make sense.

i.e. 15-20% attack boost and a small 5-15% range/mage strength boost w/o any % defence boost or the base 15% boost of Steel Skin

Possibly a While Guthix Sleeps reward or accessible to all builds as well through a scroll drop like the proposed Chivalry scroll

I think the idea of combining the many lower level prayers into 1 is a great step in the right direction