Is the tristana changes a nerf or buff?

Nerf to her early game (longer downtime on Q/shorter duration on Q).

Nerf to late-game (less AS except with Q active).

She basically loses 25.5% AS at level 18 (not 27%, as you get only bonus %-AS from level beginning with level 2). 20% of that can be regained for 5 seconds.

it is a nerf, mainly to her late game, mainly to her tower shredding. even with the active up she overall has less attack speed because of what she lost on her base.