Lets see here how is she overused.
Season 5 premiere only appeared as a villain and didn't do much other than take away Twilight and gangs Cutie Mark with only a bit more than half an episode I'll give it around 25 minutes of appearance. Season 5 finale only appeared for using the time travel speed and stopping Twilight which is pretty much only 15 minutes worth of appearance. Along with those two she had only 2 background appearances. You see only around 40 minutes worth of Starlight out of 520 minutes if every episode is 20 minutes long. Moving on!
Season 6 premiere she wasn't the focus of the episode she was sharing it with Flurry Heart with only around 1 episode to herself illl give it 20 minutes worth of appearance. Than in Season 6 episode 6 she got her first episode that she appeared is the majority of so I'll give this one 20 minutes worth of appearance. Than we have Season 6 episode 8 she technically didn't even appear for the whole episode she was acting as Snowfall Frost, but if you still want to count that as well than another 20 minutes. Season 6 episode 12 1 minute appearance fixing the Friendship Map. Season 6 episode 16 meets Thorax and only appeared for around 5 minute of the entire episode. Season 6 episode 21 another full episode to herself 20 minutes. Season 6 episode 24 a 30 second appearance in the castle. Season 6 finale first two parter completely centered around Starlight and her team so a full 40 minutes. 104 1/2 minutes out of 520 minutes.
Season 7 premiere episode 1 she was the topic of focus but it wasn't her episode so she only had around 3 minutes on screen. Season 7 premiere episode 2 she shared half the episode with the Mane 6 so only 10 minutes. Season 7 episode 4 meets Maud but it wasn't her episode so she only had 7 minutes of screen time. Season 7 episode 5 30 seconds or less of background appearance. Season 7 episode 8 name was mentioned. Finally season 7 episode 10 her first 20 minute episode. This season so far she had a total of 40 1/2 minutes of appearance out of 200 minutes.
She doesn't even come close to any of the Mane 6 or CMCs in terms of screen time. Also she is needed in pretty much all the episodes she was in. I could explain it all to you if you want me to.