This is all absolutely true. Also, to add, many deaf people receive a much worse education because the schools are unwilling/unable to invest in proper education for deaf people. So there are deaf people out there who struggle to read English because the structure of English is completely different than the structure of Sign Languages.
Also, Sign Language is NOT international. Signing in London is different that Ireland, or Paris, Toronto, Mexico, New Zealand, India-- some of the signing may be similar or even related but they are all different languages. So if you see several interpreters at an event or a news broadcast or en EU summit, and they are doing different signs, this is why.
And for the idiots who still don't comprehend that for many people English is a second language, even signers who were born in an English speaking country-- and still argue 'you get captions what's the problem' - Have you ever watched the auto-craptions on the news or a live event, or even a film on Amazon that they couldn't bother to get a human to properly provide subs? Yeah. A good percentage of the time, it's just word salad that means absolutely nothing. You're likely to just get a pile of words that may or may not have to do with anything going on in what you are trying to watch.
Some time, put on the news with no captions or sound. Put on a film or show you have never seen before, and try to lipread what is being said. Try to figure out what the plot or context is from just the actor's faces. Just try to engage when the only queues you have are facial expressions and movement on the screen-- if you can even see them talk at all, a lot of films and shows are shot over a shoulder with the back of someone's head.
Wear ear-plugs when you are out having a coffee with a friend and try to figure out what your friend is even saying. No music, no nothing-- just earplugs and trying to figure it out.
Do all of this for a week and then tell me that craptions are enough. Then tell me we don't need interpreters. After two days, you're going to be angry and frustrated because you don't know what the fuck is going on.
Interpreters do more than just tell you the exact words. They INTERPRET English language and put it into sign. They aren't just randomly throwing around their hands and looking silly. And they do it on the fly, live, as something is going. A good majority of the times, Interpreters have no idea what is going to be said. In those moments they are hearing something in English (or French, Spanish, what have you), figuring out what the best way to sign these words back to a sign-user base, and they have to do it all in seconds. It's a LOT of work.
So if you are at an event or you see two or even more signers who keep switching off after half an hour or an hour, know that the money is NOT being wasted having multiple interpreters there. They are not being lazy. They are doing a whole helluva lot, and their brains and hands and faces occasionally need a break.
So if you are hiring interpreters for an event, don't be surprised if they say you'll need to pay more to have several interpreters there. The interpreters are incredibly skilled, and they work bloody hard. If they tell you they need more than one, don't have a fit at them and try to talk them into just having one interpreter, thinking you can pay less. Understand that they work their arses off, and it's a very intense job that requires a lot of brain power and body power. So please, PLEASE be kind to interpreters.
And for chrissake, STOP DOING THIS. STOP DOING THIS. STOP FUCKING DOING THIS.