Are all weapon types viable late and post-game?
I think the reason swords, spears, and axes are so widely-used in the post-game is because that's when you really need high levels to complete grottos and such; level-grinding pretty much translates to "farming metal slime variants", and each of those three weapon types have abilities on their mastery tree that are basically essential to metal slime farming. (Swords have Metal Slash for extra damage and Falcon Slash for multiple hits, spears have Pressure Point for the rare insta-kill and Thunder Thrust for hit-or-miss critical attacks, and axes have Hatchet Man, basically the axe variation of Thunder Thrust.)
It's difficult to gauge which weapon type is best, however, because each type has various traits that make it stand out from all the others. Giving wands to your magic-users can boost their max MP and allow them to use some nifty crowd-control abilities; claws and spears both have abilities that hit multiple times, some striking random targets each time; whips and boomerangs hit multiple foes with every strike; and hammers and axes give warriors the raw attack power to dish out serious damage, highly useful for piercing enemy defenses. In other words, there's no weapon class that trumps all the others; figure out what kind of team you need for a particular task (surviving a grotto to loot treasures, take down a legacy boss, etc.) and then pick out equipment that'll cater to your team's strengths.
Swords are all round
Wands arent the best but are useful for Sages when the use Magic Burst on High level grotto bosses since they need to restore MP other than that if not equip on sage well , wait for their coup de grace since it restore mp
Fans are useful for multiatcks and matering them to omnivocational and transfering them to vocations such as gladiator make a good charactee and using Fan Dango is even better
Poles , well I dont know
Hammers , bows and spears are very useful since their ablities ( Pressure pointer , Parralx and Needle shot ) can be used for metal slime farming and legacy boss farming for orbs to make legandarh weapons,
Axes the same as above