1st. Defenders would still have the advantage in fiefs, because of the fortifications. They shouldn't have an advantage just due to the fact that the attackers can't kill enough of them in some arbitrary time limit.
2. What's the point of having population then if they're completely useless to defend with? Forcing armies to sit in fiefs is boring.
3. Yeah if you retreat it means your losing the fight and want to cut your losses, now you lose everything making retreating completely pointless and useless as a tool.
1) Makes sense, but if you want to kill an army of 1500, you simply attack it twice. There is a reason you have to pay way way more upkeep for and army of 2000 troops then 1000 troops.
2) Population does still make sense. If someone attacks you, and you have no army in there, you make sure you already have the gear on you. In 2 hours the attacker will have it known as a raid or a siege. In case of a siege you put the gear in and defend, in case of a raid you leave the gear out and lose nearly nothing, gain 24h of time to get an army there. Benefits active fief owners, if you decide to have no army in your fief its only natural that it will take more effort to defend your fief. (take for example reyvadin, 3000 pop, kapi lost the fief, and drz got it. Drz is good at strat, and used the population to its fullest, coalition had to kill every single one of the pop to get the castle back)
3) Difference in opinion. If you lock someone down for 24 hours by attacking him i don't think you deserve any compensation other then the win or lose loot you will get.