Possibly a terrible idea: what if Vayne's Q gave her defensive steroid instead of offensive steroid?

Main Proposal Like 10~30% (numbers up to adjustments, ofc) reduced damage taken for a brief period (maybe during the animation of tumbling, maybe just a flat time like 0.5 seconds). It'd make her a good duelist without giving her an insane crit burst with IE-Shiv combo. Making the defense steroid brief means that the opponents have ways to counterplay the defensive steroid (wait for like half a second). This would also weaken her trade potential early game, but still have ways to win trades by carefully tumbling the incoming damage.

Benefits Thematically, tumbling is a defensive move to dodge enemy attacks, and I think this would fit the spell better than getting bonus damage. Vayne's identity as a tank killer/great duelist would be preserved, since this means most of her damage is shifted to Silver Bolts (good for tank killing), and getting a situational defensive tool is good for dueling (basically all the skirmishers, such as Yasuo, Tryndamere, Ekko, etc). Her IE-Shiv crit burst would be removed, thus making Vayne be focused on DPS over burst. As a short ranged ADC, Vayne would have increased survivability with her new defensive tool to focus on one target while avoiding incoming damage.

Potential Issues This could be bad when combined with things like Knight's Vow, Phantom Dancer, Maokai's ultimate, and even Challenging Smite (she may be able to sustain through jungle fairly reliably by timing monster AA with tumble) that make her too tanky, but by making the defense buff last a short time would make this a non-issue, I think. If she's too tanky, it'd be from sources other than tumble, most likely.

It's also possible that Vayne can just tumble huge but telegraphed/delayed bursts like Syndra's ultimate, Talon passive, Brand passive, or Veigar ultimate. The counterplay would be to stun/snare/silence her before the burst, although it's also possible it'd be broken without nerfing the tumble cooldown. Or maybe Vayne can be a reliable counterpick against such picks/comps.

Conclusion This proposed change would make Vayne a good duelist and tank killer, but lower her burst damage significantly. This would most likely force her to build on-hit items instead of crit items. Crit itemization may remain viable, although I'm uncertain of that. However, whichever build path she takes, her damage would be focused on DPS over burst by gaining extra survivability and losing the damage amplification.