The main issue with ice types isn't the type itself. After all there are pokemon with utterly horrid type combinations on the defensive side that still manage to be OU or uber, such as Terrakion, Tyranitar or Lugia.
One may argue that defensive ice types are dommed to fail and they should all be offensive like Kyurem, Mamoswine and Weavile, but that's not the real issue either.
No, the main reason is the lack of moves. These are pretty much the only ice-type moves worth using: Ice Beam, Ice Shard, Icicle Crash, Blizzard, Ice Punch, Icicle Spear, Haze, Freeze-Dry.
These moves either have exceedingly large distribution (Ice Beam, Ice Punch), exceedingly small (Ice Shard, Icicle Crash, Freeze-Dry), require an ability to be good (Icicle Spear) or are situational/outclassed (Haze, Blizzard).
On top of that none of these moves are particularly powerful - they're good, but not "OMG GREAT" moves.
Meanwhile types like grass, bug and fire get absurdly powerful and spammable moves like Spore, Leech Seed, U-Turn, Quiver Dance, Flare Blitz, Sacred Fire, Tail Glow and so on.
Imagine if there was a truly good boosting move exclusive to ice types, or a 120 BP 100% accurate move with negligible drawbacks. That would go a long way in fixing ice types.
