I'm in the same boat as you, except that I don't feel I have attention span problems. If what I'm reading is a bad use of time, I switch to something else. If it's not, I have no trouble reading a long article or paper. I frequently read a blog post and discover half an hour later that I just read what would be 30-40 pages if printed out. It doesn't feel like a lot of reading because there's no physical page turning, but it is.
If you can consume an interesting story at 2x speed, there's no moral or personal wrong in wanting to consume it at 2x speed. Just do it! Books are mere technology: they can and should be replaced with something better if it comes along.
But doing the exercises is hard (much like physical exercise, that pain is in fact the signal that you’re making progress). And the more time we spend just consuming, the less natural it feels to work.
It’s so easy to blast through a lecture or speed read a text and feel like you accomplished “learning”. That illusion is destroyed as soon as you have to actually do something (in school, that’s usually write an essay or pass a test).
In other words, the bottleneck has never been how fast you can consume the text. It’s how fast you can do the work to internalize the knowledge.
I wonder if I'll ever be able to fix my attention span.
That said, I know for myself that my attention span has gotten shorter. I used to read more. Now I listen to audiobooks. When reading text, even engaging fiction can be a struggle. I read one or two pages and feel the urge to check something else or look at something else or get up and do something. I know this wasn't the case in middle school or high school (late 2000s).
I think it's because of first podcasts and then watching / listening to too thousands of YouTube videos at 2x speed. I've become much more "efficient" at consuming entertainment content - so "efficient" that I can get bored listening to someone telling an interesting story at 1x speed.
The only advantage I have is that I can tell that this has happened and I can work against it by forcing myself to read more. But if things were always like that, how would I know? When you're sleep deprived every day for years, you don't notice how much it is affecting you. It's the same with a short attention span.
[1]: Aside: the omnipresent talk about generations these days is maybe not the best thing to begin with.