Agree on Lucas getting over-rated. But you can rate Kane as Spurs' best player and, at the same time, rank Son higher for his contributions in 2019. Particularly when Son scored 4 Champions League knockout goals to Kane's 1, including the crucial opener against Dortmund and the 3 goals against City. This campaign too it's hard to argue past Son with his 10 goals and 9 assists so far.
The funny thing is that the poll explicitly asks who Spurs'
current best player is. I don't doubt there was a fair amount of historical achievement bias involved but weighed against the enormous recency bias that seems to afflict most football fans, I don't think it adds up to much overall.
Over the set of games during which Jose has been manager, to use a non-arbitrary cutoff[1], Kane has been better than Son on average. Son has that wonder-goal to give him even more of the flash factor that fans are attracted to - eclipsing the fact that Kane scored two screamers of his own and skillfully assisted another in the same match - but the reality is that Kane has contributed the most to the results in that time, with 2017-tier all-round play and multiple decisive goals.
Using the CL knockouts only further emphasises Kane's unfair disadvantage because he was injured for all but one game against Dortmund -- in which he scored the winner and only goal. Great goal it was too. And his no-look, first-time halfway line lob against Juve in preseason would have been a GOTS contender along with Son's if he'd just done it in the league (the level of opposition would've made no difference to him scoring that goal with that accuracy so he was simply unlucky that it happened in a friendly).
[1] It's my opinion that Kane had grown actively unhappy playing under Poch and that his non-England performances for much of the year, which have certainly been below his unplayable best for the most part, reflect that fact. His immediate revival under Jose seems to track perfectly with the theory. On his debut under Jose, he covered more distance than any other player on the pitch for the first time in ages, and I somehow doubt he was just trying to impress the manager with all that stiff competition for his spot.