Well i honestly think WE + attrition is what makes EU3 playable. The reason i say this, is because, ofcourse, when i started playing EU3 i also figured that WE + attrition is very annoying and i was thinking "hmm it has to be better without it" so i turned it off (modded it out). And guess what? It didnt get better, it was actually game breaking as blobification was ruining it. Without it, once first nation reaches landforce limit of 20, and makes that first 2 can + 18 inf doom stack, the rest of the world is done. With that army u can take on 10 AI nations, together fielding 3 X more divions than you, simply cuz ur doomstack will steam roll anything and everything.
Now a bit more related to first post, u have to see things from a different perspective. You now have the biggest and strongest (Ming might be bigger and more numerous, but ure in western tech group so u > everyone) country in the world. Ur landforce limit is probably like 300 if u made workshops in all provinces. Now imagine how powerful u would be from this point on if u could fight the rest of world one country at the time, fielding 100% of your troops each time u fight vs their 100% landforce limit. For example 300 divisions vs 100 Spain can probably mount at this point. They wouldnt stand a chance, u would simply overrun them, and even more so in HTTP where all it takes for u to actually win any war is to destroy their stacks which is pretty simple.
As u can see the whole point of this system is to slow u down once ure over 20 provs, so that u couldnt conquer the world in 20 years.
Also add 1 more thing into account. Unlike AI who thinks in a linear fashion, human player, once they understand the game mechanics, can out smart AI by factor of like 20.000%. AI think in goals and objectives given to them by scripts, refreshing them from time to time, while human changes, adapts all the time. Just remember ur first game, ur first battles, and compare the chaos from before to organized actions and tactics u can comprehend now. Every game u play u learn something new, while the AI remains the same. The reason im saying all this, is basically any country human plays has godly advantage over the rest of the world, period. Without restrictions such as WE/attrition, u could literally beat AI using 1% of ur brain power.