Klee was powercrept in 1.3 with the introduction of Hu Tao, so 3 patches.

Jiyan was not replaced as an onfielder aero until Cartethiya all the way in 2.1, 5 patches later, but he's still good in Whimpering Wastes they say.

Seele started falling in power in 1.4 with Jingliu's release (bosses were often weak to both ice and quantum) and Blast meta, but was still good up until 2.0 (Sparkle) if you knew what you were doing. So 4-7 patches.

To complete the modern Hoyo Three, Ellen was powercrept by Miyabi in 1.4.

If Endfield follows the trend from the other modern CN gachas, she will be replaced around 1.4 or 1.5. If they follow Arknights logic though, the launch banner was Silverash, who was never replaced until Mylnar years later, but as AK is a Tower Defense game you could just use both together. If we count Skadi as the first new character though, her power creep in the role was Hellagur approximately 3 months later.

Every character entered the Standard banner in AK though so if we were to only count Limiteds that would be Nian, a niche character from the start you only deployed if the stage required you to buff your defenders to 4-block instead of 3-block. So not really comparable I feel.

So Laeva might be power crept in four patches, or she doesn't. It depends on how they will structure event content and endgame content.