Accessibility - Screen Readers and TTS

Hi, I'm currently completing an apprenticeship in Digital Learning Design, and I'm working through some content on accessibility.

Previously, all our storyline courses had text-to-speech added on, but the accessibility features such as alt text and focus orders weren't used. Since I've learnt more about screen readers through my apprenticeship, I've been following correct processes and designs for best practice with screen readers. However, as these read out the text on screen, I'm wondering if the text-to-speech I manually add onto all slides is still required? 

Part of me thinks it might be too much if both the audio on the course and the screen reader are reading the content out loud, but then we might have learners with dyslexia, for example, who might not require a screen reader but still prefer to have the text read aloud.

How does everyone else navigate this? Do you use both or one or the other?

Thank you!