In the league last season for Spurs it was Kane 29, Alli 18 and Son 14 (all over 20 in all competitions). Son alone scored more in the league than any Liverpool player and Kane was injured for a spell.
United have Lukaku who'll score a hatful but Martial and Rashford will both score a fair amount and Zlatan to come in as well.
But this argument is based on optimistic viewing of Spurs/United (they won't get injuries, players who didn't score much last season are assumed to do well this, Lukaku/Zlatan will somehow both score while being alternatives for the same role); and a pessimistic view of ours (not allowing that Salah brings more goals, or that other contributors won't contribute this season).
This is more what I was talking about:
Liverpool - 13, 13, 11, 8, 7, 7, 6, 5, 3, 2, 1, 1.
Spurs - 29, 18, 14, 8, 4, 2, 2, 2, 1, 1, 1, 1, 1.
United - 17, 6, 6, 5, 5, 4, 4, 1, 1, 1, 1, 1, 1, 1, 1.
Obviously United will improve theirs this season, but that doesn't mean current trends will continue throughout the season. There's no reason to expect that Martial and Rashford are going to be 20 goal scorers. Lukaku will likely exceed Zlatan's 17 (possibly before Christmas), but it's not 25-30 for Lukaka
and 17 for Zlatan. Spurs haven't added any attacking options and their 16/17 output from that front three is about as good as they can expect. A serious injury to Kane would be significant.
But by the same token, we've added Salah, and hope to have Mane available for a full season. On last year's experience, players like Wijnaldum and Lallana contribute more than the midfield options Spurs and United have. So Spurs' profile doesn't seem likely to improve any; United's will, though by how much remains to be seen. Ours should improve a touch. But of all of those, ours is the least impacted by one or two specific significant injuries.