A frozen drink made from a recipe written for a shaken one almost always tastes weak. Three separate effects push in the same direction, and all of them have to be corrected in advance.
Why cold mutes sweetness
Perception of sweetness falls as temperature drops, which is why a warm soft drink tastes cloying and the same drink over ice does not.
A frozen drink sits far below the temperature of a shaken one, so the same quantity of sugar registers as noticeably less.
Acidity is affected less by the change, so the balance shifts toward sour as well as toward thin. Both need addressing, not just the sugar.
What the ice contributes beyond cold
Blending with ice adds water to the drink, and the quantity depends on the machine, the ice and how long the blender runs.
That dilution is larger than what shaking produces, so a recipe transferred directly arrives weaker in every component rather than only colder.
Consistency is the harder problem. Two batches blended for different lengths of time arrive at different strengths, which is why bars standardize the process rather than the taste.
Why air changes the texture and the flavor
Blending whips air into the mixture, and that air is what gives a frozen drink its light body rather than the density of a slush.
Aeration dilutes flavor by volume in the same way it dilutes color, so a well-aerated drink needs a more concentrated base to taste equivalent.
It also affects how the drink holds. A drink with more air separates faster in the glass, which is why frozen serves are built to be drunk immediately.
How sugar affects freezing itself
Sugar lowers the freezing point of a mixture, so a sweeter base produces a softer, more scoopable texture rather than a solid block.
Alcohol lowers it further, which is why a high-proof frozen drink refuses to set properly and stays loose no matter how long it is blended.
Recipe development therefore treats sugar as a textural ingredient as much as a flavoring one, and adjusting it changes both at the same time.
What that means for adapting a recipe
The practical approach is to build the base at a stronger concentration than seems correct, then blend and taste the finished serve rather than the mix.
Acid usually needs increasing alongside sugar, since a sweeter base without more acid arrives flabby once the temperature drops.
American frozen classics were developed in this order rather than adapted, which is why they tend to work as written and adapted recipes often do not.