Hm - If I take the Alpha Cards than I see that water had already two magic monsters (by the way also other splinter had already two magic monster), so if you have the Medusa with 4 (3 + Summoner Buff) and the Mischievous Mermaid with 5 ( 4 + Summoner Buff) damage the Frozen Soldier is away in the first round, they do 9 damage and the Frozen Soldier has only 6 life points - and the Magic Reflect make not enough damage to kill one of them.
So I think against magic attack the Flesh Golem with void was also in the alpha-version much stronger than the Fronzen Soldier and as I told in the fight monster against monster he would win in every case.
I play also alpha-card-tournaments and I can tell you that if you would do a statistic the Flesh Golem is sure more in use than the Frozen Soldier.
I think that the Spineback Turtle is also more in use than the Frozen Soldier but I don't wanted to compare them cause they have different Mana-costs (4 to 6) and sure one of the reason why the player take more often the Spineback Turtle as tank than the Frozen Soldier is that than they can use this 2 Mana at another posiiton.