Frost Shamans are the core unit of Tundra Orcs. They are cheap and have a high life. Their inconsistent damage may be off-putting and it’s not great on it’s own, but paired with tools like Influence, For Glory, Targan or even Brutal Force, it gets the job done.
When in doubt about what to summon, Frost Shamans are a solid bet as they are efficient and a cheap threat.
There is a big incentive against Tundra Orcs to keep the board filled with cheap units to avoid the multiple high damage tools the Tundra Orcs have, in that context the damage of the Frost Shaman is more than enough.
However, if your opponent is summoning high life targets, Frost Shamans will not be very effective and Smashers should replace them.