Franks are the easiest civ to play.
Very smooth economy and generally very simple army composition, particularly in team games - make scouts in feudal and make knights->cavalier-> paladin, get some throwing axemen to counter pikes if needed.
There are some areas where they struggle, but they're definitely baby's first aoe2 civ.
Franks have strong winrates in closed and open maps on all ELOs in ranked, and in tournaments.
Not sure what the dev is talking about there re: economy, the faster berries and the free farm upgrades make them so smooth to play. The cheap castles are crazy as well.
Faster berries and stables only came after the 2013 HD edition. Before that, they had a food+gold heavy army that was supported only by free farm upgrades and a UU and UT that were bad value for money. In Feudal, their scouts lacked bloodlines and were 20hp down despite being a cavalry civ and in imperial, they lacked and still lack archers and their skirmishers are gimped without the bracer tech. They also lacked squires which meant all their infantry moved slower and so became more susceptible to ranged damage.
Before the FE mod / HD edition, they were one of the worst civs in 1v1 tournaments and a worse pick than Persians or Huns or Mongols or Spanish for teamgames because all of them had much better economies and team bonuses.
He's talking about the pre-2013 age, which could be called age of the Huns, because they were the commonest pick by far in 1v1 games on open maps.