Interesting. Every adventuring party around me have at least one each of single class Wizard/Sorcerer and single class Cleric. Most of those players are playing RPGs for years and have some experience of playing older DnDs. So they know how important to have them.
Regarding the survivability of low-level arcane casters, I have two advice for those players.
1st, do not play Elven Wizards. Wizard is their favored class, but it does not mean that they are good as a single-class wizard. Try Dwarf or Gnome. Having high Constitution score is very important for those arcane casters. Or, try Halfling. They do not have Con penalty as Elves do, and Halflings have the best AC due to it's size and high Dexterity score.
2nd, in DnD, a party should fight as a team or they cannot do things well. So other members of the party should try to protect party Wizard (or Sorcerer) from melee attacks. I wonder why 8 men party can't do this.
Regarding Clerics, well, if your party is big enough, try to have more than 2 single class Clerics. Remember good clerics or neutral clerics of good deity can turn any of their spells (except for those in domain slots) into cure spells. So in 3e, they do not need to fill all their spell slots with cure spells. Now they do not need to act as pure medic and can have a lot of opportunities to cast other spells.