Worth pointing out that we have yet to sign someone to fill Fellaini's spot in the squad, let alone Herrera's. It's not like this would neccesarily be our only midfield signing, especially if it was at a reasonable price.
Also, I'm not sure I buy this idea that we need to make absolutely massive strides to get a top four place. To challenge for the title? Obviously, that's years away. We were only five points off fourth this year though, even with our early season and late season collapses. Since then at least one of our top four rivals have gone backwards, losing their star player, losing the manager and being in the midst of a transfer ban.
Given the glaring holes in our squad, it shouldn't be that impossible to improve the amount required to get fourth. I mean not having Ashley Young as your starting RB is nearly worth five points in and of itself, let alone anything else. Strengthening isn't just about adding talent, it's about adding structure and coherence too.