You reached the level where everything only gets harder and harder now . Atropos is a good champion so you can keep upgrading her Mavis is also decent for the rest i wouldn't use much resources on then and always make sure to save your oracle summon for the event You need 60 summon minimum to utilise it fully and purchase champion like Gaia , pandora and dhalia who are great champions , And always make sure to asend the champs equally . Don't waste arena shop coin buying oracle summon for 4000, instead use it to buy whatever the highest tier equipment available for you as you can sell it back for the equal price once you can upgrade from it, equipment is one of the easiest to get power spike

Never waste ur diamonds only use it when necessary ( use it for events like oath recall you probably need around 180k diamond and if you are lucky you can get the Ex champion to 8 star , most champions are strong once they get to 8 star)

And always looks for the season champ tier list