I don't have a problem saying I didn't feel he was easily expendable. I did feel he offered something offensively they didn't have at the time (and they've really yet to replicate). As much as he's a passenger in midfield (or at least not willing to do what they need him to do), I do feel he gave them something they still don't really have in outside shots and creativity. I think a healthy Keita could provide some of that (less on the shots, but more the unlocking element to prime-Coutinho). I do think Fekir would have done most of what Coutinho could have brought. I also know most of my grumbling was considerations towards the fact that he was going midseason, when they didn't really have any lined up replacement, and grumbling before the season, when they had no idea Salah was going to be the Salah he was in 17-18.
I'm also not sure it's fair to say that anyone could have really projected some of the development the entire squad has made. In 17-18, Andy Robertson is on the bench still for most of the first part. Trent really hadn't grabbed his spot. There's no big Virg till January. There's no Alisson. No Fabinho. That Liverpool roster is much less dynamic, and really, the dominance and power of the midfield hadn't fully developed. So, yeah, I have no qualms saying that his going was going to be a big hit. They've clearly mitigated what he did for them by improving elsewhere.