Agree that cell count must be the same. The charging current however will be not be evenly split among the batteries, but rather according to their internal resistance. So in the above case the 5000mAh and the 2200mAh batteries will receive different current, not 5amps both.
When parallel charging with a simple parallel cable you should charge only batteries that have roughly the same voltage, otherwise there will be a very high current between the packs. A paraboard with some overcurrent protection on each branch is definitely safer, if not all batteries are at the same charge level initially.
yah i guess if you have a "dumb" charger yes you have to take care of yuor connectors. have a look at PowerLab 8 and you'll see why this application based chargers is fully autonomous