Here are a list of the Power Rangers I think who are kind of overrated:
Tommy Oliver- Yes he has to be the most overrated of all time. He was an extremely likable character. So he went from sixth ranger to becoming the "Big One" of the Power Rangers series while maintaining a rash personality. His partnership with Kimberly Hart was a popular one which its break-up caused a huge HUH reaction when in Zeo. His return in Dino Thunder became a good reason for older fans to watch the series. He was also known for performing dangerous acts like fighting Lord Zedd one-on-one (but he never killed Lord Zedd). When playing Sentai Dice-O, choose Dragon Ranger, Kiba Ranger, Oh Red, Red Racer and Abare Black to form the "Tommy Five" team.
Zack Taylor- He is one of the coolest characters to be ever established and one of the toughest (but he's not as tough as Trini Kwan). He had a huge fanbase that when he left, Adam was just a shadow to him.
Trini Kwan- She is the first yellow ranger in the Power Rangers franchise. Okay so her Zyuranger counterpart is really male hee hee. She was portrayed as a woman who was hesitant to fight but she was a powerful and skilled martial artist (IMO in almost the same was as the late Mika Koizumi who was the first yellow ranger in Bioman). She had a huge fanbase one way or another which when she left the show, some fans bashed MMPR in general because she was a pretty likable character. They felt Aisha was just a shadow compared to her. IMO she's the most likable character ever to the point that when she left, it was a sad moment. I guess it had to do with Thuy Trang's issues with payroll that she had enough and quit that this fine character left.
Jason Lee Scott- The first red ranger was a fan favorite by many that they felt that Rocky De Santos was nothing more than a shadow compared to him. He was one of the most likable characters and personally, as a Sentai-PR fan, he reminds me of some of the most likable Sentai characters like Kenta in Maskman and Daichi in Turboranger which may contribute to his personality development. Sadly he left during season two. His return in Zeo for awhile as Gold Ranger was something that pleased fans. Sadly he didn't stay for long with those powers until the final battle.
Kimberly Hart- She is one likable character despite the initial start of her as a valley girl. She had a very good chemistry with Tommy Oliver which made her popular and the two had a huge fanbase. Unfortunately her actress Amy Jo Johnson left the set because of personal reasons (and she was given a proper send-off) so soon enough, she and Tommy were broken up with what I consider a badly written episode of a "Dear John letter" which angered some fans. It caused them to bash Katherine Hillard even more. It's revealed she and Tommy are still friends after the break-up in the Turbo movie.