More crippling overspecialization and the concept of weakness

Here's a theory I formed in the middle of a game when one of the enemy assassins decided to chide someone on our team for building defense against him. I won't repeat to you what he said because it's words like that that get people permabanned. What you should take away from that encounter is that building defense against him was somehow seen as a weakness rather than adapting to threats. It made me wonder if the extreme focus and popularity of assassins is because of that, the idea that not going all in is somehow considered a weakness.

I've gotten very jaded and tired of seeing everyone want to go all AD melee assassin and then ironically no one dealing damage or being a threat, much less scoring kills simply by having nothing to contribute to the team if they have no answer to the enemy having superior tanks, crowd control, ranged abilities, etc. The support is depended on to not just prioritize utility over firepower, but also expected to pick up what the rest of the team cannot or is unwilling to do. Depending on how short-sighted your team is, this leads to the support doing.... pretty much everything, INCLUDING the damage that the rest of the team decided to focus on. It's become so commonplace I'm starting to wonder if this is willful blindness; I stopped mentioning it to people, I stopped pointing it out because no one wants to think about it, so long as they think they can achieve great glory from killfasting the most killfastest.

Is this really the case, though? Are people seriously abandoning most of the game's elements simply to look like the biggest bully on the playground? Do you really think being the tank or building any sort of defense is some sort of weakness? I'm starting to think this is the case, if not a conscious decision definitely a subconscious one. The problem is so many people do it, so many lack the forethought and hindsight to think about what the team as a whole is lacking that any setbacks become seriously daunting when your only known or available gear is to try and muscle forward.