Pseudo-Supports
Psuedo-Supports are champions that people play when they get support and still want to do big damage. Frequent champs picked as pseudo-supports include Veigar, Fiddlesticks, Annie, Vel'Koz, Lux, Zoe, and especially Brand and Zyra. Some of these champions are better at being supports than others and honestly pseudo-supports aren't even bad. Lux and Zyra are practically secondary support already, but a lot of them aren't very good supports enven if they end up the best player on the team.
Now that the definition is out of the way, the problem that we seem to encounter is how these champions are played. A lot of people play pseudo-supports because they ended up with the support role in draft and want to still do damage instead of play an "actionless" champion. In my opinion, this isn't inherently a bad thing. However, when people end up playing a mid mage support, they buy a spellthief's edge and then just play like they're in mid lane. This causes an issue when the adc, who already doesn't have a true support to help them, doesn't get support-like help from the psuedo-support.
Support champions are intentionally made to help the team is a non-damage oriented way, especially the adc while in lane. In early game, the idea is to help the adc get strong fast since they are the late scaling damage. They bring healing, resistances, utility, and crowd control. Pseudo-supports are usually mages who are made for mid lane casting and not supporting. While most champions that players bring as pseudo-supports do have decent CC, it doesn't end up really being used in favor of the adc. Most people will just play the champ like they would in mid instead of helping the adc get strong.
And herein lies my biggest concern. If, let's say, Veigar support does mid Veigar things in bot lane and gets a majority of the kills, he will get pretty strong. That's a good thing for him, and by extension the rest of the team. However, the more kills the Veigar gets, most likely the less kills the adc will have. This means that the adc will not scale very well, if at all, into late game. Now most people will counter with either the adc is bad or that the Veigar will just carry and that isn't really what this is about. It's about strategy and team composition. Most likely, playing a pseudo-support already gives up on healing and utility in favor of damage, which can be great for team fights and lane pressure, but it ends up being a problem when that damage is used for personal gain rather than helping the adc.
In conclusion:
ADC champions start off fairly weak and scale very hard into late game. Supports are meant to help them in lane to quickly scale into late game. People who play pseudo-supports typically don't really help the adc and focus on furthering themselves. If they do help the adc, then they typically don't scale like mid mages, which means their usefulness come from their utility which many lack in. Supports get a support item which allows them to scale into late game without need for kills or farming. Instead, they help the adc get lane and kills, allowing the adc to scale into late game. Pseudo-supports get a support item and scale into late game on their own. However, taking kills instead of helping the adc get them causes the adc to get left behind and have a harder time scaling. So basically, when a psuedo-support plays like a support, you get a strong adc with a mediocre support, but when they play like a mid laner, they become a strong ap mage with a weak, almost useless adc.
TL:DR
It just seems like pseudo-supports don't really contribute as much as real support in any case. Either they play like real supports and end up scaling damage poorly and having to rely on what little utility they bring, or they play like a mid laner and end up getting really powerful, but starving out the adc and making them down a champion.
As usual, all comments are welcome, in agreement and opposition. I just ask that it is constructive.