What im about to say wont help you further because you dont have acces to the mons (yet) but this is the team i used.
With a dual race companion i clear the boss stage in 2 turns which saves some time. I think i need about 2-2.5 minutes for a stage depending if i pay attention or am doing something else.
What i do here is just wait for lowemon and metal, in the boss stage i use the damage abilities on susan and use shakamon so i can use lowemon and metalgarurmon for 2 consecutive turns.
if youre looking for a companion the best choice by far is metalgarurumon X-antibody as @bilaterus said or his other variants who are DM, they all do the job the exact same way except for the holy variant and/but metal is more common to get as ally.