I was looking for a mod that worked well for leveling crew members but both available alternatives (Faster Crew Leveling and Learningallthethings) have their downsides: the former is too overpowered and the latter is cheaty because it applies a passive random chance to level to single pilots and it's limited to player owned npcs. So I took experiences.xml file and tweaked most entries.
The scope is simple - to balance what is intrinsically broken or underpowered. It is an experimental work based on number tweaking, so it may need further testing. Most changes are relatively small to ensure better consistency in progression tables. Since experience table is shared with AI, the final result should make better pilots and traders (technically speaking - closer to 3 stars in a long run), and that includes your enemies as well.

Summary of changes

• Tweaked X4 Level cap - FCL was uncapped in all the modded variables, I changed most caps with the following order: bad 9 normal 12 good 15.
  
• Buffed piloting Killing a ship is now capped at 15; turrets, modules, and other smaller structures will contribute much more to piloting skill and are capped at 12, same for other combat events (disable, repel, flee), divided in two tiers, easy/normal (12) and hard (15).
  
• Buffed Mining and Trading, minor nerf to Station Trading - it makes trading and mining a viable alternative from gamestart. Station trading is actually quite good, it has been toned down a bit in line with most actions
  
• Revised morale buffed in group actions, aligned to piloting for a more coherent progression
  
• Engineering has been slightly buffed in most non building activities, just too add some source diversity and make xping a more harmonic process
  
• Boarding has been slightly tweaked: individual boarding xp has been increased; group boarding has been reduced a bit due to morale changes
  
• Tweaks to non combat actions ship repair, dismantle, construction, upgrade
  
• Better skill curve with less difficult average levels to reach; most skills will contribute to level progression. To my calculation you should be able to reach 3 star pilots/marines/traders in 50-100 hours; 4-5 star crew will be still very rare
  
  
  

Vanilla Issues
- For efficient leveling the player is bound to abuse one broken mechanic (Ship Builders, Xenon spawn area, chain-boarding, Trade Station, Terraforming); most of them are late game solutions, and buying a skilled pilot costs more than a XL ship. At that point of the game crew level becomes just a money issue (I'm a space billionare tyrant but most of my personnel is mediocre, why?)
- In vanilla game Piloting is really difficult to raise without a solid action plan and a decent fleet grinding spawn points. This happens because of two things: most triggers have a terrible exponential falloff with a very low base value and a low level limit - this makes them almost irrelevant for the leveling system. For example destroying a surface element has a 0.21  falloff, that means that after roughly 2 stars its contribution to leveling is negligible at best
- Not all actions have the same time required for a single skill check. It is impossible to fix this without a script (for example adding a script where you can't trigger a success more  than once every X minutes)
- Most actions have an hard cap and become useless for high trained personnel
- I applied the geometric distribution formula in order to simulate the number of average attempts required for a single success to occur and applied it to my tables (basically a*b^c with the relative percentage of the event, assuming c between 0 and 14). I compared them with an average game situation at 100-200 hours according to saves I had the chance to grab and analyze. This was the best way to approximate and measure the variation of the falloff value and its effects. Bear in mind that most of  triggers will work regardless of crew level, so grinding may speed it up further. That means the you may reach a couple of good 4-5 star pilot in less than 100 hours. Due to exponential nature of the formula, 4-5 stars should be hundreds time faster to gain but still extremely slow (for some skills chance was like 1/140.000.000!)
- Same concept applies to ship Trading and Mining. Without the mod, both activities are subpar to trading stations. With the increased xp it becomes a feasible alternative and you won't see 5 stars managers in less than 10 hours while you're ship traders will struggle to go beyond the first star; instead you should find both 3 stars managers and pilots at the same time.

Mod Pro
- Proactive approach: you'll need to do things, no passive XP
- Adds diversity
- Killing things, trading, mining: 3 main actions to improve your level of piloting, engineering, management
- Every action counts
- You won't max your crew in 10 hours
- Seminars will still be useful and buying personnel will still be a thing
- Most of imbalances have been toned down

I suggest to use this mod alongside my second mod, Balanced NPC Hiring Fee.