I don't think people are particularly criticising the teachers who are forced to do this as well as a full time teaching role. BUT people are criticising the system. And the shrinking resources.
This is why I tend to favour bigger schools, they have more chance of squeezing money for someone to concentrate on the role.
In my experience: Secondary SENCO is absolutely fabulous, but is a real rarity: works extremely hard, cares about the students, knows her stuff and has a fabulous support team who get the admin done.
In other schools they've gone from okay at the admin, and go through the motions to pretty good and understand what they are doing.
In Primary we had a SENCO who was full time, good at the paper work etc., but admitted she didn't know that much about the different SENs, she had specialist staff for that - possibly why they could be okay with mild dyslexia but not so good at educating those with ASD (and some things didn't get spotted).
However I do find this a bit worrying: "The staff in my school are all dedicated to doing their best for all the children but we are restrained by staffing, time and space. Some specialists just don't get that when they come to advise us." For the same reason as the OP - sometimes things are requested by parents and every "specialist" but are not created, such as a "chill out place". Of course if they are forced to create them, schools will then show them off as an added feature and a sign of the creative problem solving - I know a school which has done exactly this.
LarrytheCucumber - you sound like you were a good SENCO (as much as you could be) - and lots of people are desperate to find ones like you - who will listen to others and ask advice.