The tokens that Daxos the Returned creates can quickly get out of control. In the end game, 3 mana to create a token is extremely powerful, especially when it is an Enchantment itself. There is an awkward interaction with cards like Opalescence and Starfield of Nyx that reduce their power and toughness to 0 due to the fact that they set power and toughness to Converted Mana Cost, and tokens have no mana cost (unless they are Pack Rat tokens which have a converted mana cost of 3, but that’s a rare case). However, having Enchantments like Glorious Anthem and Intangible Virtue which pump creatures allow them to at least have 1 or 2 power and toughness. But those two Enchantments don’t really synergize with Daxos.
Erebos, God of the Dead, Helios, God of the Sun, and the aforementioned Athreos do play well with Daxos, being Indestructible Enchantments that can become creatures with enough Black and/or White mana symbols on the board under your control. Also, cards with the Constellation ability are extremely good with the amount of tokens that Daxos can create. Doomwake Giant, Grim Guardian, and Underworld Coinsmith are Enchantment Creatures that can give you good incremental advantage over time. Skybind, another Enchantment with Constellation, lets you “blink” non-enchantment permanents to reuse enter the battlefield effects, although it’s hard to say how many nonenchantments you’ll be running, so it depends on the build of your deck.
In the 99, Daxos could be a good ally for Zur the Enchanter. However, Zur’s ability to put an Enchantment directly into play doesn’t synergize well with Daxos’ experience counter ability. It’s hard to say exactly what other Commanders outside of White/Black could use him effectively, although many White/Black decks play a great many Enchantments that Daxos could help you benefit from. However, like a good many Legendary Creatures created specifically for Commander, Daxos the Returned is best utilized as a Commander, built around for maximum effect.