Sony knows what they are talking about. But do you think Makita just decided to ignore the datasheets and charge the cells at whatever they feel like without first getting the thumbs up from Sony? Sony would have stopped supplying them long ago if that. The 1c reccomended current is probably already a compromise between cell life vs charge speed, and 0.5c is even better. 0.2 for overnight charge is probably best. But doubling the reccomended charging rate most likely introduces an insignificant amount of additional degradation, thats unavoidable anyway. It doesnt mean squat in real life.
And remember these datasheets are for the end user, that can choose to charge them with anything from a dumpcharge from another battery, a homemade or a cheap chinese copy of a chinese copy of a chinese charger, and given this, no manufacturer will say "yes of course Jim, our cells will take 5A current but make sure you have a good extinguisher". Theyll play it safe and state 1c max. Manufacturers that buy millions of cells, are probably getting a sheet with different values.
Bottom line is, you worry about nothing. 4A charge for a 4Ah pack is 1c anyway. For a 2Ah is 2c. Keep the cells cool and its fine. Its not the high charge or discharge current that kills the cell, its mostly heat. Fast cell degradation starts at 70-85°C, not at high currents.
