Morgana is not a full ap support because if she was building to support her adc she would build to make her spell shield be more effective or build to make her abilities have effects such as slows with Rylai's or Twin Shadows but she obviously needs Zhonyah's for her ult.
Brand is a full ap support but he is also a good support because he uses his burn passive to synergize with Rylai's and his ult is most effective in a lane with more than 1 person and he has his stun that he can proc with his passive.
Lux is not a full ap support because if she was building to support her adc she would focus her build around making her shield as strong as possible and focus on engaging with her root.
There are many other "full ap supports" aswell such as Zyra, Orianna, Fiddlesticks, Swain, and even Veigar, all these "full ap supports" are very good and effective because they have a kit that is either cc heavy, has massive AOE cc (veigar), or they work better in lanes with 2 people (also veigar with his passive ap scaling).
also your not really explaining why it is "no fun" for either side i mean at least explain why it is not as effective as a healing support, tank support, hooking supports, or heavy cc support instead of just saying its "no fun" because that's not exactly a valid argument against full AP supports.
also the only items you listed that i ever see being build on full ap supports are Sorc boots or Liandries usually but off the top of my head only brand comes to mind when i think of a full ap support going Liandries, and the only times i ever see supports going Morello is when they are laning against a soraka or another heavy healing support.
I have never heard of a support that's not trolling that goes Archangels or Void staff.
The certain "supports" i dont believe should be played by anyone who isnt trolling is champions like Vel'Koz, Zoe, Neeko, Cho'Gath, Cassiopeia, Malzahar, Karthus, Xerath, Annie, Sylas, Mordekaiser, Teemo, Malphite, or Shaco (maybe shaco but I have not had any good experiences with shaco EVER working as a support)