Most of the C1/L1 improvements are real improvements over the Ex1/X8E1/T48 series of rifles.
90* gas port hole erodes less over time (reference Ak47 vs AKM).
The inch pattern gas block is arguably a dramatic improvement over the Belgian design - gas adjustment knob and front sight system.
The Belgian Ex1/X8 2 piece gas nut/carry handle sleeve is stupid - having to unbreech the barrel or remove the gas block to remove the gas tube or carry handle is stupid.
The butt stock "wings" on the Ex1/X8 belgian butt stock cracked and broke out.
I'm not sure that the 2 angle bolt locking surface matters (the Indians used the single angle bolt to the end with their IA1 rifles) - but the 2 piece extractor is a major improvement over the long tail flat wire spring BAR pattern of the Ex1/X8.
I used to prefer the Ex1/X8 pattern pistol grip, but have come to prefer the inch pattern angle and shape.
Having said that, the US pattern (T48) flash hider adopted with the C1/L1 is ungainly long.