It's relative. Viv wasn't a bad player of spin, but IMO Tendulkar is in another league.
In general, Indian batsmen from 70s to 2000s were the best players of spin that I have seen.
They approached spin like a workman treats his lunch. You could almost sense the glee in their eyes when they came across a spinner.
One of the reasons why (psychologically) I can't have high regard for Warne is because of the way Indian batsmen treated him series after series after series.
I have never seen an ATG (of that level) as utterly helpless as Warne was against India repeatedly.
Coming to Viv against spin, perhaps what transpired during mid-1980s impacted my thinking.
In the 1980s and even into the 90s, SCG (Sydney Cricket Ground) was to spinners what Perth was to fast bowlers.
Even at the peak of their domination, West Indies couldn't win a single Test match at SCG,
their best were draws in 1982 and 1993 (thanks to Lara's 277).
Viv's scores at the SCG during the 80s were:
44, 22, 15, 58, 11, 4
Except for the first Test match in 1982, Viv got out to spin there every time.
Even in the subcontinent, in both 1985-86 series against Pak, and 87-88 against India, he got out mostly to spin (6 out of 10 times).
It could just be my thinking as well. Back then, whenever I watched him bat in spin-friendly conditions, I just never felt the kind of comfort that I got from watching Tendulkar (or many Indian batsmen) under those same conditions.
Again, I am not claiming that Viv was weak or useless against spin, but to me Tendulkar (and many Indian batsmen from 1980s-2000s) were simply in another league.