Traveller gets a bad, often false, rap... CT Advancement, and ONLY CT, is super slow. (Yes, even in the '77, there is provision for learning new skill levels... taking 4 years to be effective, and 8 to be permanent.)I suspect you are right - Traveller has notoriously ‘flat’ character development. I picked up Pirates a while back but when I run it I will be using Savage Worlds.
Mongoose's first flavor has a rather nice in-play growth. A number of "weeks of study" of a single skill equal to the character's total skill levels gets you a new level in the studied skill; awarding a week for good RP is also recommended. This latter makes character growth stable and steady. once per total skill level sessions, less if getting goal awards.
Only Classic Traveller is really slow at advancement; MegaTraveller's gives way more skills in play than in Char Gen, but not for the first year of the character's life in play... but then you get the third advancement tally in a number of skills and sudddenly pop new levels...
TTNE uses an XP to buy new levels model.
T4, tick all skills used, one of them gets rolled for at end of session. More if you hit goals or roleplayed well.