?
They are all really strong even without a heavy AP build. If you think about their early game and they are against an equal skill adc they may and probably will lose (mid lane,), you put then bot lane, and the enemy has an actual support and adc, and you might have some problems
How do you deal with this stuff?
Mysticman891 votesYou play safe against them (perhaps losing cs, but better than dieing), until their base damages aren't enough to be a threat, then you proceed to win the game as a side effect of (hopefully) having a support that can still offer utility, while they just have an assassin that can't assassinate, and so is almost useless. One of the main mistakes people do against unconventional supports (such as assassins) is to play normally (e.g. playing as if the supports damage is almost negligible), then they get fed, and then theres a problem.
Ekko might not be the worst since he's still got his aoe stun, but the other two have minor knockups/displacement/slows that make them almost useless as supports.
Jetjoe1 votesThis is true and your points are valid but there are some scenarios such as 
support. I just find soraka so useless especially late game since she gets deleted with her support.
She cant peel or do damage either
Mysticman891 votesGood rakas are quite difficult to kill, since they can position themselves relatively safely, won't actually spam their heal to the point a sneeze can kill them, will be able to kite those who dive her with her Q (which also heals her and slows the opponent), and can use her silence to ruin most assassins trying to dive her (and/or use her E in the direction she's running, so people can't chase her without getting rooted).
Meanwhile she's one of the handful with a global ult, so she can turn around fights from across the map, and can foil peoples assassination attempts on other players (e.g. carries) using similar methods to the above.
People are bad sometimes is all, but pretty much every champion can work when played well pretty much regardless of the match up.
Flaherty1 votesWhen you play Soraka positioning is super important, make sure they can't reach you because they will need to focus you otherwise you can keep everyone else alive. Throw your silence in front of people going after you and they won't be able to reach you easily.
Jetjoe1 votesSo it requires a good soraka, for someone in bronze-gold elo supports like Sona, Morgana, Braum, Thresh, Blitz are probably better
Beldair1 votesAs a Support main, I've considered trying an Ekko support to broaden my support roster....but I don't pick him because of how my team is... Usually I get teams that want to report me for doing off meta supports... Like Mordekaiser...
Mysticman892 votesWhen you're playing supports, particularly off-meta ones, you have to ask yourself "what utility do I provide?" and remember that you're going to be more or less useless outside of that utility since you have no cs/kills in theory. I'll play almost anything support (luc, kat, yi all seem useless utility wise) as a result, but in most case theres a pretty good reason why off-meta picks are off-meta.
Morde offers a situational movespeed boost, and some limited healing for a teammate. Not exactly a stellar resume for a support compared to other options.
Ekko I'd consider messing around with as a support and could see it being semi-viable. Still better options (e.g. meta stuff), but probably workable, as he has a slow, and an aoe stun, the latter of which is pretty high utility.
67chrome1 votesAssassin Supports ?
Not the best idea.
If they don't win lane hard, they become a 5th wheel, falling into a position where all they can do is splat into enemy champions like a bug on a windshield.
They are all really strong even without a heavy AP build.
They still need some kind of build to do things though, which they have trouble affording as a support.
A lot of conventional supports like Thresh, Blitzcrank, Alistar, and Janna can still be a huge thorn in the side of their opponents with no items.
Jetjoe1 votesThey arent perfect bt they do so much damage that their adc can just knock off the enemy as if they last hit minions.
I did a brand and pantheon bot lane once and we beat the living shit out of the lane that they became irrelevant. Today I was blitz supporting jinx, and I Wasnt sure how to protect my jinx against their miss fortune and fizz since fizz can tower dive being as broken as he is.
67chrome1 votesThey arent perfect bt they do so much damage that their adc can just knock off the enemy as if they last hit minions.
So does every champion with a burst rotation, including a wide range of conventional supports.
Today I was blitz supporting jinx, and I Wasnt sure how to protect my jinx against their miss fortune and fizz since fizz can tower dive being as broken as he is.
You pull MF into Jinx's traps, pretty nasty combo. What's Fizz gonna do?
Zitoshi1 votesI once did 
+ 
bot lane and Zac was support, it was actually pretty awesome because we would just all in and kill them over and over and it was so hard to actually kill us.
zlumpy1 votesYou know who is even more annoying in bot lane? Rengar with an early sweepers and cordination with his adc. He just deletes people and you dont even have to get that close to the bush. Then again throw a leona at him and you'll see who rules the bushes in bot lane.