This is exactly my experience too. Sometimes it's incredible just how little applicants understand about how to develop software. I've even interviewed people where they were allowed to have a web browser and IDE while coding a solution, and they still struggled.
Personally I am a much bigger fan of using FizzBuzz as a gate than an algorithm question. I think algorithm questions optimize for the kind of developer who doesn't mind memorizing algorithms to get a job, which might be a useful skill, but you can test that same skill of memorization using FizzBuzz, and then you don't end up also filtering out people who can code but don't care about memorizing algorithms.
In any case, I always think it's worth using their solution as a jumping-off point to ask other, more language-specific questions. Things like: how would you change this if it was intended for use in a FizzBuzz library, how would you annotate this if you needed it to be injected as a Spring dependency, why did you use a for loop instead of a Java 8 stream (or vice versa), what are the implications of declaring this thing as final or static, can you write a unit test for this, and so on. That's when you can get past the point of memorization into figuring out if they actually understand what they typed, which is helpful to ascertain their level.
No, it's just an opening to discussion. For example, depending on the experience of the person, it might lead to a conversation about dependency injection in general, the transition from Spring-specific to JSR-330 notation, maybe they can give some examples of where Spring-specific annotations are still useful, they could talk about constructor over field injection, or when it might be better to use a static/pure function instead of a bean, all kinds of stuff.
For me there are basically two questions to answer when I am interviewing someone. The first is if they have any real programming ability at all, which hopefully FizzBuzz should answer. (Many people do not pass that threshold.) After that I'm looking to figure out where they could fit into the team, or the company. That means seeing if they are already familiar with the frameworks they will be working with in the position (usually, but not always the case for junior applicants who have held at least one job before), but then also if they can speak critically about some of concepts used in those frameworks, and perhaps compare different approaches that have been taken to solving similar problems over the years (if they are more senior).
It's not a wrong answer if they don't know the framework or the concepts behind it at all, since they might be switching specializations, but that's important to know at the interview stage because they might be better suited for a different role than someone who is deep in the framework and more likely to be able to hit the ground running.
Personally I am a much bigger fan of using FizzBuzz as a gate than an algorithm question. I think algorithm questions optimize for the kind of developer who doesn't mind memorizing algorithms to get a job, which might be a useful skill, but you can test that same skill of memorization using FizzBuzz, and then you don't end up also filtering out people who can code but don't care about memorizing algorithms.
In any case, I always think it's worth using their solution as a jumping-off point to ask other, more language-specific questions. Things like: how would you change this if it was intended for use in a FizzBuzz library, how would you annotate this if you needed it to be injected as a Spring dependency, why did you use a for loop instead of a Java 8 stream (or vice versa), what are the implications of declaring this thing as final or static, can you write a unit test for this, and so on. That's when you can get past the point of memorization into figuring out if they actually understand what they typed, which is helpful to ascertain their level.