I think that whole idea to this patch is to force players to retire and change their builds. Because of strategus, everyone is high level and in strategus everyone wears plate which means that massive strat battle lasts longer and gives insane amount of XP. With more agi oriented builds, we'll have less plate in strat and battle will last shorted therefore giving less XP.
Really? Did you even look at the requirements before making this post?
Gothic plate and Heavy Plate armor only require 15 strength.
Which means at level 30 you could have a 15:24 build with 8 WM & 8 athletics.
This will result in people being faster in plate with less HP, this means you will be able to kill more in the same period of time (ranged will be more effective due to people having less HP on average and people who stick with strength builds will only need a couple hits to kill people in plate). This will increase EXP not reduce it.
Also strat battle time limits are controlled by the number of tickets not the equipment so even if people did start bringing less plate (which most if not all factions will have already bought), the battles would last the same length of time.