I think the main source of frustration comes from the fact that the balance team tends to balance around competitive play and mostly treat lower-elo play as secondary, as they usually should, and also tend to address issues at a different pace than Boards, so while many threads here complain about Zed/Tahm Kench/Illaoi/etc. needing nerfs, they read the patch notes and see Lulu/Talon changes seemingly out of nowhere and feel like they and the balance team are playing two entirely different games -- and they are, to some extent, it's just that the balance team is grounded in hard data that they're often not a part of.
While I think the balance team is absolutely right to prioritize high-level play, and that they do have valid reasons for not going too deep into balance levels at gold and below, which tend to be a lot less stable and often more dependent on large differences in skill or experience than raw numbers, it's a shame that they haven't really looked into opportunities to improve things there too. Many changes made by the balance team tend to address issues with champions at high-level play, but often to the detriment of their general enjoyment. Champions like Rek'Sai or Lulu should feel good to use at all elos, since they have relatively simple mechanics overall, except they feel underwhelming until you get to fully understand the "real" power behind some of their mechanics (e.g. Rek's detection, Lulu's safety), and champions like Azir or Ryze only become truly playable, let alone viable, at the upper tiers of play. Often their nerfs or buffs don't really make these champions more accessible to newer or less mechanically intensive players, and that tends to lower enjoyment overall and make the game's learning curve even steeper. Perhaps this might be a design problem as well as a balance issue, but Riot should look into more ways to make champions feel better (and sometimes worse) at lower elos without affecting high-elo play, and they've already had success with some instances of those, like the changes to Alistar's combo reliability or to Lee Sin's passive and ult a while back.
for AP, whereas AD has 
, 
, 
, and even a 
could be considered defensive to some extent.
brings the spellvamp issue, 
is only considered if they have a lot of tank, 
and 
, while powerful, don't fit the current meta, but that's not really an issue with the items themselves. 
is just super greedy, but isn't really considered useless, 
is another item that's really only viable on a small handful of mages.