If something is streakier, it has more streaks or lines on it.
Streakier can make people think of messiness or unevenness.
Examples:
The streakier window was harder to see through.
Her painting was streakier than mine.
The sky was streakier today than yesterday.
The more I tried to clean it, the streakier the glass got.
The more colors you mix, the streakier the paint becomes.
The more I ran, the streakier my face got with sweat.