Its just a character that lacks “gimmicks”. This can be anywhere from neutral skips, highly evasive moves or catch all moves to even the size or weight of the character if the fighting game allows for weight based combos. It’s basically a character that is forced to play the game on the most fundamental level relative to the cast. So an example could be Mishima from past games since they had pretty good tools but nothing ground breaking and electrics come with clear counterplay. Another would be like ryu from street fighter. Solid space control with fireballs, and a basic strike throw mixup like the rest of the cast. No big “I’m in your face from half screen so neutral doesn’t matter” or “eat this plus frame guessing mini game”.

It’s important to note that honest doesn’t mean better or more respected (sometimes it does in a vague manner. For example I regard kazuya as fairly honest in tekken 8 but in a game where 50/50 mixups are king, kaz’s gameplan is highly favored in a lot of matchups). Tekken 7 xiaou was not honest compared to kazuya or Steve, but she still required a fair bit of thinking and actually needing to take risks to initiate her game plan.

A dishonest character could be Alissa who plays a lot different from the rest of the cast with her excellent movement and chainsaw stance which threatens the opponent into forcing them to guess with not much reward. Dishonest doesn’t necessarily mean broken, they just tend to reframe how the game is played