I hope you're right and he's shit. Liverpool seem to be on top of the data situation, though.
This is correct. They have a data driven transfer policy, doubt if he will turn out to be a complete dud. The most we can expect is, he wont match Mane/Salah's standard as those standards are very high and even if he did, its going to take him a few seasons to take-off and that should stutter them. Also, Mane/Salah/Firmino all peaked together. That's not the current situation. By the time he peaks, Salah could leave and again there might be a big void for them even if he takes-off by then.
Also Salah, as good as he has been, has a selfish streak in him. There will be teething issues considering Salah's ego. For a younger player from a different league, its going to be harder for him to go gung-ho without resistance from the likes of Salah, Jota, Diaz. A bit like the Coutinho situation, their front three were flailing because it had to go through him as he was their top dog! Same happened for us with RVN not accepting Cr7.
So its not all cut and dry. Another rebuild phase, which might prolong for 2 more years for them (Due to Salah leaving again next season). So there is hope that it might take longer for them to get back and we could catch up or go close by then, why NOT.