I think everyone is bigger now, so no one stands out as huge. When I was a kid lots of players were really skinny and used skills to get by (smoko and pie at quarter time break) whereas now you are more likely to be a successful player by being super fit and have reasonable skills. Most players train to this goal. Also height is an advantage, so players look lean compared to say Rugby League players (who look like, as the saying goes, a brick shithouse).
It really is a running game. The AFL did some GPS tracking of players and got average 13km ±2km (8 miles ±1.2 miles), with some claimed max. 20km (12.4 miles)
Some internet research:
Basketball 2.72 miles (4.4 km)
American Football 1.2 miles (2km)
Tennis 3 to 5 miles (4.8km to 7km)
Soccer 7 miles (11.3km)
The current PED controversy is organised peptide supplements by teams, without player knowledge or consent: