User blog comment:Aphostropils/Questions from a beginner/@comment-5035765-20160405022324

1) probably already been covered by someone else, but ADCs need to have that weakness of being squish, otherwise they end up REALLY hard to kill, since they're the best class for Lifesteal. It'd be near impossible to ever duel them (which is why all champs made to duel are melee range or at least short ranged, so that they're kiteable).

2) Buffs and Nerfs by RIOT, for the most part... it's all a matter of players finding the OP stuff, lol

3) already covered why Tank ADCs aren't a good idea in #1 (I mean, TECHNICALLY we have 2, in Graves and Urgot, but both of those are built more as Bruisers than like true Marksmen due to their short ranges). As for Support ADCs, the problem with those is that Supports are supposed to survive on very little gold, while ADCs are the most gold dependant position in the game. However, there is one champion who is a Support ADC: Ashe... BUT her supportive qualities are QUITE weak (a weak slow on her attacks, and a stun that works best when used far enough away that it'll pretty much be gone by the time you get there.) and she's rather immobile for an ADC (with rather low damage from her abilities, to boot)

4) Depends on your position. But yes, you should always have some flexibility in your build. For example, you won't be building much MR against an All-AD team (except maybe Spirit Visage, but that's more for the passive than the MR, lol). Likewise, you're more likely to want % penetration against a tanky team as a damage dealer, as opposed to flat penetration against a squishy team. Most champions have CORE items that they HAVE to build, but other than that, adapt to your situation (honestly, a problem a lot of lower rank people have is that they simply copy some pro's build rigidly, with no adaptation behind it, or actual knowledge of WHY it works).