Not entirely true.
While i ultimately build the same 5 core items (one of which is the decision of BT or BotRK) there is also the choice to build a defensive item (GA, banshees, mercurial, randuins, frozen mallet, etc...) or an additional offensive item (second PD, BT/BotRK, ghostblade, etc...).
That's not a huge decision either to be fair. The most important note is WHEN an adc builds an item. I.e. do you build IE, t1 boots, PD, T2 boots, BT, LW, defense; IE, PD, boots, LW, BT, defense, etc... most notably when to get boots, %pen, and lifesteal as all are important in different ways.
Less notably but also important is the fact that a BotRK rush is **easy ** whereas an IE rush can be hard (you may not be able to afford a BF sword in a Lane trading heavily). While vayne can rush her easy-to-build optimal first item in any game regardless of how often she's forced to base, almost any other adc is forced to deviate from IE if they are forced to base with less than 1550g repeatedly. There's only so much you can do (pickaxe, second dorans, boots, vamp sceptre, etc...) before you run out of inventory space and need to complete a first item that isn't IE. vayne literally never has this problem with BotRK.
With critical strikes being weakened (randuins change) I'm hoping to either see compensation for crit based adcs or nerfs to the strong non-crit adcs (vayne being at the forefront, with corki and ezreal being potential champions to keep an eye on). By non-crit i mean those who don't rush IE.