I'd bet what I make next month that the advice given to a 2L to get bespoke suits and the notion that the law firm looks at a rookie lawyer as a "rainmaker" is coming from people who have never set foot in a real law office.
If you put fifty lawyers under one roof, you will have the gentlemen who know what style is and spend the time and money to get it. You will also have extremely valuable partners who view the whole process of acquiring and wearing suits as simply a necessary function, no more important than selecting between one egg in the carton and another. While the bespoke suit might - MIGHT - impress the former set, it will do little or nothing for the latter, and there is a risk of coming off as a dandy when what the partners want is a workhorse, not a dressage animal.
The comment above is quite right that it is the technical expertise, which is a given by the time the firm writes you a check, and the ability to function within the existing ecosystem that will determine the young lawyer's fate. The bespoke suit won't save or conceal the diletante or the primadonna.