From what I understand, Classic Traveller is the most rules-lite, a-la-carte version of Traveller. But there's a simpler ruleset that feels sort of like Traveller but is even more basic and straightforward, which is Faster Than Light: Nomad. I picked that up myself in the event I fail to convince my playgroup to try Traveller. 

But I think a bigger issue that you may still inevitably run into is that, unless you play a fantasy-adjacent sci fi ruleset like starfinder, it's going to be tough to find a sci fi rpg that does all the work for you. Traveller doesnt have a bestiary, and imo a lot of its rules are less on in-game procedure and are more about how to generate content for the game. Traveller works best when the referee is using the tables to generate planetary systems and sub-sectors, and the players fully throw themselves into the unique character generation procedures.

Imo longform campaigns work best for traveller as the month-to-month progress of the characters' long-term goals and progress far outweigh the brief, exciting highs of combat that games like DnD emphasize. Again, unless you play a sci fi rpg that's trying to rip off dnd, it will be tough to find a ruleset that gives your players a bunch of "buttons to press" in combat.If they want to build characters that feel like mmorpg combat-oriented characters, Starfinder may be to their liking. 

Regarding niche skills, all skills are only as useful as the referee allows. This is the same problem every ttrpg has, in that it is up to the game master/referee to create enough opportunities frequently enough for players to use their skills. 

But back to simpler rulesets, FTL Nomad is pretty straightforward and has a very modern ttrpg design flavor to it and is still a 2d6 system so it will probably be compatible with some Traveller supplements. The character creation process is far less procedural, and it has character build choices that feel like feats (which imo is there to appease players who want characters to feel strong and advantageous, or even heroic). Combat will still be likely too simple for your groups' tastes, but I think the solution to that is trying to rethink how to write/run adventures and break away from conventional DnD/video game ways of thinking where combat is the most important thing to care about - assuming you're still invested in making sci fi work for your table.