My biggest beef with AoS is that GW has made it so damn easy to buy into multiple armies.
Back in the WFB days 8-15 orruks or ghouls didn't do squat. You couldn't play a game of WFB with just those models. The force wouldn't meet the hero/unit requirements and I doubt those low numbers would even meet the unit block minimum requirement. These barriers would stop one (well, me) from even buying a handful of cool models to begin with because I knew I wouldn't be going all in on a full bore army.
However...here in AoS...the philosophy is 'play with what you have!' I can buy a group of Ironjawz and run them in a low count AoS game....or use Skirmish rules. And it's easy to do this with all the factions. "lemme just buy a few here..." Next thing you know you have 5-8 different factions you want to expand on. Then a new cool unit/model comes out for another faction and you're again back to "lemme just buy a few..."
But I must hold. I must allow the FEC to be my Death army of choice. I must....