Welcome to the great pet,familiar, mount, etc disconnect in D&D type games. A lot of archetype fantasy character concepts depend on the character having one or more critters around. Mage's familiar, Ranger's companion, Paladin's mount to name a few. Yet these critters often die fast and often once combat starts. Doesn't even take AOE. Magic Missile is a great familiar killer in earlier versions of the game. And the loss of the familiar often imparted long term serious disadvantages to the Mage. Later versions limited the dead familiar penalty but it would seem the Familiar's Union would at some point lodge a protest over the high death rate.
And Mounts and D&D are a joke. A couple of kobolds with short bows can take out a 20th level Fighter's standard horse. Not sure how critter drawn caravans ever get anywhere. One attack by monsters or thieves and half the mounts are worm food.
Part of the problem is the way HP are handled in D&D type games. The characters get fairly rapid HP increases via leveling and further benefit from AC increases due to stat improvements, leveling(for some classes), and equipment. Yet the critters are often stuck with their starting HP. So while a 1st level Fighter may have similar HP to a basic mount, the 10th level Fighter could well have 8 to 10 times more. So any viable threat to the Fighter renders the mount a pile of goo.
One off the cuff solution is to have mounts, familiars and other character related critter receive HP corresponding to the level of the characters. Mount of 1st level character gets(don't have my books handy) say 1d8+5. The mount of a 5th level character gets 5d8+25. That way the critters have about the same chance to survive an attack as the character does. This "mount HP effect" is a function of the character not the mount. So if a 10th lvl char trades his mount to a 1st lvl char, the mount goes back to a 1d8+5 mount.
Another option is have characters pay a 'critter leveling' cost to increase a mount or other critter's HP. Cost could vary according to wealth in the game. So a 1st lvl mount might cost 10gp while a 10th lvl mount might be 1000 gp or in a high gold game 10,000gp.
