The problem a bottle has to solve
Fresh tea changes within hours. A drink sold in a bottle or can must stay stable for months, without clouding, darkening or losing its aroma. Nearly every difference between bottled tea and a fresh cup follows from that. Heat treatment for safety changes the aroma, and the chemistry that makes a cooling cup go cloudy has to be managed, so a producer works with a lighter or filtered extract, and may add acidity or other ingredients to hold the drink steady.
Unsweetened, low sugar and sweetened
Sugar and acid do a lot of the work in a sweetened bottled tea, covering what processing has taken away and making a thin extract taste fuller. An unsweetened bottled tea has nothing to hide behind, which is why they tend to be made carefully, and why they are a large category in Japan. Read the ingredients in order, and check the sugar per bottle as well as per 100 ml, as bottles vary widely in size.
Sparkling tea
Carbonation makes acidity and astringency more prominent and lifts aroma, so a tea that is merely pleasant still can become quite sharp when carbonated. Producers often choose light, aromatic teas and cold extraction for that reason. Sparkling tea is often presented as a non-alcoholic alternative to wine. That is a description of the occasion, and it is not a claim about what is in the bottle.
Concentrates and syrups
Concentrates are strong extracts designed to be diluted, used widely in cafés and bubble tea shops because they make every drink the same. Their strength and sugar vary greatly, and a label reading tea concentrate does not tell you how much tea it contains. They are a sensible tool for consistency, and they are not the same thing as brewing to order.
How to read the label
Look at where tea sits in the ingredient list, whether the word is tea or only tea extract or tea flavouring, what acid and sweetener have been added, and the sugar in the whole bottle. A bottled tea can be a very good drink, but it is judged by different standards from a pot of tea and should be.