I think Miracle Cheer is likely the best weapon.
Pros:
BiS for Soul Voice, (potentially)Marcato for non Honor March
Lets you do ~17-18 mins of SV songs.
Not sure how less potency is bis for soul voice and devs said no duration stuff stacks with the 15min duration. It's 15min.
He meant that you can reapply SV songs again after almost 3min of SV active and reset their duration to 15min again. You dont need Troubadour for song duration, so nothing stops you from doing that. Normally when SV is still active after 2min+ you cant reapply songs like that, because without Troubadour you would actually put 5min songs instead of 10min+. So its almost 3min+15min with Miracle vs ~
1114min with Carn+Gjallahorn. If you do event like Odyssey or anything else that last longer than 15min, getting SV songs with 1 less potency for 18min is easily better than SV songs with 1 more potency but
11 14min.
EDIT: I realized you can still put nonNitro songs with SV and reapply them with NITRO ~3 minutes into SV. That is a risky strategy tho. If you fail to reapply with NITRO, you will end up with 5min SV songs. If you fail to reapply with Miracle, you still has 15min SV songs.
It also let you EASILY put 15 SV songs in 3 parties if needed. Because you are not bound to NITRO duration (so you use NITRO in the first party just to cast last song, which is honormarch. Then switch to party#2, put 5 songs up fast, then switch to party#3 and start with honormarch (after that, you dont have to be worry about NITRO anymore, since rest of the songs will be 15 minutes anyway). So NITRO is only needed to be up from last song in party#1 to first song in party#3, instead for all songs for all parties. All songs beside honormarch will also last longer.
Its also amazing QoL for something like dynamis.
DD in your party died 2min after you did NITRO songs? What you do normally? You apply 4 songs to that poor guy using Piannisimo 6 times. Now he has 4x 5 minutes songs. So you will need to sing 5 min songs again in 5 minutes for whole party (destroying Marcato song for everyone beside that DD), or just rebuff this guy again using 4x Piannisimo. Then in another 3-5 min after that (depends what if you rebuffed whole party or one DD) songs on rest of the party will start to wear, so you need to do another NITRO rotation. TONS of wasted time.
Now what you do if you have Miracle? You can ignore +1 potency and simply rebuff whole party (including raised DD) with 15 min songs and just Piannisimo Honormarch on raised DD or if you care for +1 potency on minuets/madrigals, you can just rebuff 5 times to 3x15 min songs and 5min honormarch on that one raised DD. All you will need to do till next Nitro rotation is Piannisimo honormarch this raised DD once.
Now you can make it even easier if you completely ignore +1 potency (
+7 Victory march and Honormarch is still enough to cap magic haste, so all you will lose is 12 attack and 6 acc on Minuet V and Blade Madrigal or just 12 attack if 4th song for farming is Scherzo. Thats almost nothing) and use Nitro rotation just for Honormarch (and Piannisimo not being required for reapplying songs to dead people), making your life SO MUCH EASIER.