>>224449
>>224480
>>224525
Non-casters are definitely viable. They won't be the most powerful member of the party, but they are useful and do contribute.
Many of the best spells, and certainly the most spell-slot-efficient spells, are buff spells. These are a lot better when cast on someone who is good at fighting to begin with. Haste, for example, is probably the best level 3 spell wizards/sorcerers have when it's time to kill things, but it's only good when there are some big burly friends around to cast it on.
Non-casters also have a much longer "adventuring day." With cure wands everywhere, they just top off their hp after a fight, and they're just as ready for the next one as they were for the last. True, this is mostly useless - if one member of the party wants to keep going but everyone else is out of spells and wants a nap, guess what's going to happen. But occasionally there will be situations where the party has to push forward anyway because the situation is urgent. At those times, they will be glad to have someone who doesn't burn through very limited resources to operate. No, this does not happen often enough for the non-caster's endurance to equal the caster's power and versatility, but it does happen.
A lot of people will say that tanking is useless because if the monsters are played well, they'll just ignore fighter-types and go right for the casters. There's something to this, but casters have a lot of spells to make themselves difficult to reach or target, and a good portion of fights will usually be happening in tight confines with a lot of narrow corridors and choke points around.