For all the reasons already listed as being the canonical makeup of the character, it absolutely is an inconsistency.
Your post amounted to
- Boba Fett is a clone.
- Boba Fett is related to Rex.
- Boba Fett got put in a box by Ventress.
You cannot just list points, without providing an explanation on the traits they demonstrate, and then claim it shows inconsistency.
We have seen that as a kid, Boba Fett was still guided by his conscience and sense of honour. It makes sense that as an adult, he would look to rule in a way that is different to a sadist like Jabba.
This is a legit possibility, even though its more likely BoBF simply didn't get the same budget for cgi and stunt work that Mando did.
Budget doesn't determine the results though. Chun Li still looks imposing and she's in the same series. I legitimately think he's recovering.
Also worth mentioning that he effectively lost his tribe. That he is still going is a sign of how hardened he is. However on some level, you'd expect someone to try and replace that loss which would explain the recruitment.