Bazylka, I use Metal in my team, and tbh your can't really go "super fast" in dungeon unlike other game modes... specially now with the unbelievable scaling ... the hp of the opponents gets too much to be 1HKO by your atk, Metal sure helps with this (but you need a Metal Ancient, for highest possible Vengeful sword damage) ... altho, you do have to take an atk for that, and if you were following other dungeon thread about Highest Possible opponents, you'd know that it's really difficult

But, if you can work between a KO oriented team, and a Quest orient team...
With a KO oriented team, where you basically survive for high KO counts, Metal works really well, two divines + ancient + earth + water are good element combination, also Like I said, you need to have a metal ancient for this, coz the Vengeful sword damage is boosted significantly once you use it after using leech (with wonder/accept. sigils ofc) . Although with such teams, you don't really get a lot of quests done, but you end up making up for it by getting KOs, and I find this team consistent with the average number of stepping stones you can generate.
With Quest oriented team, where you making focus on getting quests done for stepping stones, you just replace metal with AOE element (light and/or fire preferred) while leaving the rest of the combination almost same... This team being quest oriented, is faster (as dungeon run end faster) but I find the average number of Stepping stones generated by this to fluctuate a lot, coz you have to rely on quest rng to give you good quests.
I have both kind of teams (fortunately, with only 5 max level dragons), I start the dungeon with KO oriented team to get as many Kos as possible to reach those KO bonuses, then I switch to quest team to make my run faster (basically die quicker lol) .
But I stick with KO team more often (or when I'm not in hurry) coz like I said, it's more consistent.