More of Vayne's damage should be on Silver Bolts than her Tumble
As her "Identity Spell," Silver Bolts is what should make Vayne a late-game horror, capable of tearing through even the beefiest of tanks.
However, Tumble is far more beneficial to her damage output (until you reach said ultra-beefy levels). I believe that it should give less damage to her next basic attack, and that Silver Bolts should hurt more instead. This would not only increase the time window for non-tanks to not get blown up, but also increase her overall difficulty. Tumble is already an exceptionally good repositioning tool for an ADC to have, reducing the scaling of it would help enforce high-risk high-reward.
Bad news for Vayne: This would make it harder to Vayne to assassinate people overall, as she would need to proc Silver Bolts more. Overall, she would need to rely on Condemn stunning the target, or risk chasing them over a greater distance.