Aegon didn´t wipe out everything (5k out of 50k), but his enemies didn´t have "I am losing, but I won´t give up yet" modifier. You know, that one, which doesn´t allow you to enforce demands even though you reduced their army from 30k to 2k, sieged half of their land and imprisoned everyone and their hamster.
So, making big dragons kill almost whole armies only helps, because your enemies will give up sooner. Otherwise (especially with shattered retreat), kings Mern Gardener and Lorren Lannister would return at least 4 times for 4 other Fields of Fire.
And yes, this happened to me with small dragon, who wasn´t able to destroy such huge amounts of troops. And enemies were returning and returning, only to lose again and again and again and even though I sieged more land than I wanted (it was de jure war) and won every battle, they still wouldn´t give up, because it wasn´t on 100%. And thinking that I would experience the same with Aegon (who also had much smaller army than his enemies)...well, let´s just say I completely agree with those 95% losses.
