Well... when I think of both classes, they both have their own fun ways to combo around the map...
TBH, I'd say Thunder Breaker. Not becayse Hayato isn't good or anything, but because Thunder Breaker can maintain their maximum number of achievable buffs while Hayato's Willow Dodge is a really iffy buff that isn't exactly easy to maintain for the damage it gives him. In comparison, Thunder Breaker mostly just has to maintain a steady "combo" to keep their Lightning Counter up and the boost of damage from comboing skills together and using... whatever the giant red tornado is called.
Though on another TBH, I don't remember TB all that well. Though I did level up Hayato lately, and I personally feel he has TOO MANY attacks that can all still be utilized well into 4th job, where Thunder Breaker has just enough attacks to do everything they need to do.
I could do without a reminder of how copy-pasted Jett used to be.
I honestly believe you over-exaggerate and, brutally honest, do not understand the class at ALL.
First off, Suborbital Bombardier was literally a copy-paste of Corsair's Eight-Legged Easton, but for the longest time without hyper skills or any of the updates that ELE received over time. It wasn't even the best 4th job skill at the time.
Second off, I can't recall a single person who thought the old Jett was even fun, let alone any good, myself included. And I have yet to hear a single person who misses the old Jett, probably because NOBODY misses the old Jett. If you were to put the Old Jett in Maple now, even if you updated the skills to modern standards, Jett would be laughable and ignored. The class had no redeeming qualities, and it didn't take anything from Bucc or Corsair that would make her unique.
Third off, it's not "dashing around", it's combo dashing RAPIDLY to get to where the enemy is, forcing them in front of you with Cosmic Upheaval if need be, and then to use Planet Buster, Falling Stars, Starfall, or if all those are on cooldown, Backup Beatdown. Two of the four are POWERFUL skills, one of them is surprisingly powerful and effective and comboing to get to even more advantageous placement, and the last is a skill that starts weak at first, but gets improved the moment you start getting hyper skills for it.
Third, while I don't know what world you are in, it took me, a Reboot player where all the enemies take longer to kill, almost no time to get to level 150 as a Jett. I won't claim I didn't spam Starfall, because I did, but my eyes are still sore from all the spamming and I did revert to the classic "position, reposition, kill, repeat" movements. But it took me, keeping in mind I am only a casual player who plays for like 5 hours a day, about 3 days total time, and most of the time was spent doing theme dungeons and quests. I say "total time" because I only played Jett when I was done on other characters, so I only got anywhere from 2-4 hours playtime on Jett a day. No EXP buffs, no burning, not even EXP related link skills. Just my own abilities and, after 4th job, Starfall. Oh, and like 2 hours of 2x event, but I spent most of that time trying to get a Mr. Ali familiar.
I admit Jett does have some damage problems, but she wasn't designed to be a heavy damage dealer. And you know what, I honestly believe that's fine. If you want damage, then you clearly should be playing something like Aran or Dark Knight. But she is probably the queen of mobility, and I do not say that lightly. She makes up for her inability to finish battles fast by getting to the next battle faster than any other class, when she isn't forcing the next battle faster than any other class. In the old days, all she had was whatever could be lifted from Buccaneer and Corsair, of which she probably got the worst of both their kits at the time.
Also, I'm not a Jett "main". I prefer other classes over Jett simply because I've become invested in those classes long before I played Jett again.
Again, I don't think you understand Jett at all, and I think your favoring old Jett means your own playstyle does not mesh with the Jett we have now.
A burning character is a character that is participating in the Burning Project event. ( It will be available on July 5th.)
Only new characters can participate, I think.
I think any character from level 1 to 150 can be burned actually. The option to burn a character usually appears under eligible characters during the event period.
