I honestly don't think Kane or Son is the problem of Spurs, they were 1st and 3rd goalscorer of PL last season, they were leaders of the league and the ones who carried this club. If they are provided with plenty of support from others they can easily lead the league in goals and carry this club to glory, as they had such little support from middle, they just had to feed one another with assists, they were 1st and 3rd in assists, too.
The real problem lays with lack of creativity in the middle, in short, Spurs failed to replace Eriksen.
Spurs spent more than 100M Euros on Ndombele+Lo Celso transfer, but neither of them really replaced Eriksen, that's the bottom line of Spurs problem. This lack of ideas and creativity in the middle is the reason of Spurs struggle in attack, Spurs just don't have a playmaker on the pitch.
When we had Eriksen Spurs usually excelled opposition in possession, nowadays we can't even win possession against likes of Palace and Wolves, let alone making crucial chances, it's so severely lacking that Spurs are rock bottom 20th in chance making. In current environment it's hard to produce results even with Kane and Son.