If Freezing/Burning became easier/ more viable, Serena Grace users (and possibly Ice moves) would probably get banned entirely. This is because the status conditions are not equal. Freezing (and to a lesser extent Burning) is already a much more severe status alignment than Sleeping and Poisoning.
Firstly, you cannot do anything whilst frozen. Paralyzing and Burning have two effects (stat lowering, para chance and loss of hp) but the Pokemon can still function despite these flaws. When a Pokemon is frozen it cannot do a damn thing, basically becoming a sitting duck. But why is Sleeping not so bad then? (ok, there are Fire moves you can use to thaw yourself but that would demand clairvoyance or using really subpar moves to use effectively).
Because there is a upper limit on how long you can Sleep. A Pokemon can Sleep for a maximum of 7 turn (which is A LOT) but it will usually be far less than that. Freezing have no such limit, meaning the Pokemon will not only be a sitting duck, you have to rely on chance for it to come back to life. And heck, you can do stuff whilst sleeping! Of course unless you inflict it on yourself with Rest it is ill advised to carry Sleep Talk, but still.
The low chance of Freezing occurring in the first place is what makes it balanced. That fact you cannot rely on freezing happening, ever, is what makes it balanced compared to Burning, Paralyzing, Poison and Sleeping. As the best status condition it need to have the biggest drawback.
Thirdly, immunities. Only Ice types are immune to Freezing, which is huge. Fire and Electric types are commonplace, and so are Steel/ Poison. Nothing is immune to Sleep by without an Ability, but again, maximum 7 turns. If Freezing was ore common, half to all of all team would be an Ice type, both to inflict Freezing and the other half to prevent Freezing on your own Pokemon.
If there was a 60% chance of Blissey freezing its foe with a single attack, it would get banned immediately. If there was just a 10% chance of freezing being undone, it wouldn't be a major deal, but would still be a little bit to good. Freezing would basically become a more accurate OHKO move, more or less permanently incapacitating anything. If there was a upper limit on how long one could be frozen, or you could do something whilst Frozen, or there were a lot more Pokemon immune to Freezing, I could could see it getting a buff, but as Freeze looks now, it needs to be hard to inflict, to not become to good.
TL/DR A Freeze chance of 60% would be absolutely broken, and banned on the spot.