If you're getting spammed, then your opponent likely has better footwork and timing than you do. Some weapons ARE more viable as spam weapons than others (longsword, katana, nodachi, glaive, etc), but these CAN be countered with better footwork and timing.
I get as pissed off as anybody when I have some scrub with one of these weapons left click me to death, but they were only able to do so because I did something wrong and didn't play well enough.
Stamina is a TERRIBLE game mechanic unless the game's combat is based around it from the very core level, and even then it's VERY difficult to implement properly without making one single combat style infinitely better than all the others.
A resilience skill would not work well, especially based off strength. Strength glaive spam is already horrendously annoying to deal with, and adding a skill that makes them able to shrug off hits even better relatively than they can now (seeing as others would not have this skill as high, they would have a longer stagger time) would be terrible.
