I'm actually doing some research on this at the moment. There are a number of things that have been going on behind the scenes that you might not be aware of.
First, the proportion of jobs that are allocated 'Welsh essential' (WE) in local authorities will vary from county to county according to the different circumstances. So, for example, in Gwynedd all internal communication in the authority takes place through the medium of Welsh, so anyone working for the authority will need to know Welsh (because otherwise they won't be able to do their job, whatever that is). In contrast, here in Cardiff only a small proportion of the jobs are allocated WE.
Second, all local authorities have recently had the Welsh Language Commissioner's Standards applied to them, which have various obligations (again, varying from county to county). Part of these are that the county needs to be able to provide a Welsh-language service to its residents that require it, and many of them are finding that they don't have the staff to provide the necessary cover. So, for example, here in Cardiff any front-line service (e.g. reception area) needs to have at least two Welsh speakers on the team so that at least one of them can be there at any given time to cater for any Welsh speakers who might arrive. That is why many new posts are being made WE where they perhaps weren't before. Another aspect of the Standards that has had an impact here is that each new post must be assessed for Welsh language considerations (whereas previously it wasn't obligatory to consider it when the post was advertised). Also, people working for the authority can request that their internal training be provided through the medium of Welsh, so some authorities are finding that they need more HR/training staff who can speak Welsh. And so on.
Third, 'Welsh essential' doesn't necessarily mean 'completely fluent to native speaker standard'. It will depend on the job, but it might be that what is required is that someone can hold a basic conversation, rather than being able to explain the complexities of planning law (or whatever). Often, the 'Welsh essential' comes with 'or be willing to acquire the skill'.
But most organisations are also very keen to use training to help the existing staff acquire/improve Welsh skills, because they will always want to keep existing staff rather than recruit new. All the people I've been interviewing for my research are desperately keen to provide a service to Welsh speakers that is at least approaching that to English speakers, and to encourage those with some Welsh language skills to develop their confidence, and to persuade them that their Welsh is 'good enough'.
I'm sorry for the screed! But I read so much rubbish online (that 'you can't get a job now in a local authority if you don't speak Welsh' and that 'they're only doing it to keep out the English') that's so counter-productive, and really quite untrue.