It wasn't, but that's because basically nobody in their right mind would consider *you should bomb blocks everywhere to find out if they're interactable* a fun mechanic, so of course when we're given a different implementation that vastly decreases the tediousness, it feels "balanced around it", despite the ubiquitousness of it in the series prior to that point. If you added the pulse to old games, they would similarly immediately feel balanced around it.
I respectfully disagree with you on this one. Older games (Super Metroid, Fusion, and Zero Mission specifically) used a ton more visual cues to denote where a lot of the secrets are hidden. Plus Super Metroid also gave you the scanner eventually, which was similar in function.
Samus Returns had smooth walls everywhere with a lot less visual cues to denote secrets because they wanted you to just use the radar instead. It wasn't as great from a level design perspective, but I do think the game was
balanced around it.
Regardless, in all the games, it became easy to find the secrets once you had the super bombs - they pretty much cleared the screen and revealed the nature all of the blocks anyway. Walking into a room and laying a super bomb wasn't considered "easy mode" or "unbalanced". So why is the radar thingy? It's the same function without the destructive element.