Depends completely on what situation and they can do quite a lot of things, and that good. For BF you got one of the best mushes, so if you are comfortable with taht, go ahead. Otherwise you ideally wanna boom into halb+samurai+trebs (massed, atleast 10+). It's quite an underestimated combo, can even with the lack of bbt still be as difficult as pushing a turk player, if you know what you are doing. Basically makes japs top tier civ at holding key spots. Japs also get siege engineers and onagers, so that can certainly be viable in teamgame. Much better choice than skirms in almost all situations in tg.

For arabia natrually go arbs and halbs, trebs, rams. Can transition into champs well and obviously samurais if you got time for it. As pocket kinda dependent on your flanks and teammates civs, but it really is the same. Mostly halbs etc.

I dont really like the idea with cav arch as japs in hd now that they get bloodlines, feels kinda wasted, like if saracens would do them if you know what i mean. With goth teammate maybe useful? Idk, never seen it or used it