Even right now we are in pre-season stages but look like Liverpool is not learned from their previous mistakes and allow few good players without any suitable replacements even I read they are in talk about few players but still they are doing few things quickly without any cover which can hurt them again in coming season just like they have done with Sadio Mané and face trouble throughout season and lost their spot as well.
Now allowing Fabinho and Henderson without any quality replacement surely going to hurt them badly as McAllister is also not fully fit, and they are doing poor in early matches as well, hopefully we will have few quality players in middle of the squad which will help them for having better performance in the coming season.
Liverpool lost several core players in this season's transfer window such as Firmino, Fabinho and captain Henderson. Now leaving these 3 players certainly leaves a gap for Liverpool management to be overcome immediately in this transfer window. We'll be looking forward to seeing what changes kloop will make in the one month remaining of the transfer window before it closes in September.
So if you look at Liverpool games in pre-season matches, of course they didn't show a more impressive performance when they faced Bayern Munich because it was clear that there were many gaps in weakness in their squad. Bayern munich was able to beat them even though they lost Sadio Mane, but Bayern Munich performance in this match was quite impressive. But for kloop he seems to have found a weak spot in their squad after being left out by Firmino, Fabinho and Henderson.
Liverpool to me have oversold their players in this transfer window and for the fact that the session is around the corner makes it more obvious that the club may be taking a rather hard route this time because just as you rightly said getting a replacement for those players will be a tough quest for Liverpool.
And if care is not taken, Liverpool may have a bad season again in this premiere leagues, even though the previous season also wasn't all that colourful for the club where their struggled to stay in the top 5 o the league table.