ok , that's right endless game must be end at some point.
but attacks from outside which you can't do anything about them >> Catapult bombardment from Valor's rest , Totems from Rage Valley , Sand Whirlspool from Ruins of Nas'de etc...)
sometimes they really screw the game balance on earlier waves.
for instance on KRO i made through wave 64 without using gnome items , but after that i played lots of times with the
exact same strategy , i couln't pass wave 53-54 most of time. Also couple times i lost on 40's. Because catapults were really mad they didn't stopped bombing , and entire screen filled with webspitter spiders along them.
So luck is a real factor if you able to make higher levels or not. If you are lucky you may reach 60+ wave on valor's rest with a powerful hero. But when the catapults goes mad and webspitters starts to rush... say good bye.
also , i've been curious what the hell is spiders doing with gnoll army? it's totally out of concept.