Action economy IS the balancing factor in 5e, generally. Most battles last 2-3 rounds so the more you can shove into those 3 rounds the better it is for you. My understanding on A5E was that the goal was to add more options without increasing power. This ability lets you do everything a Bard could do before in o5e plus add 1d12 temporary hitpoints to someone every round of combat or give one of you allies +5 to all their saves every round of combat.
It gets used up pretty quickly but if you only have one random encounter per day then who cares? Even if there's more, stop and rest for an hour before continuing and it is fine anyways.
You will turn off certain concentration spells when you do it, true. Which is weird enough as it is since all the Battle Hymn effects all last only one round. There's no one round concentration effects anywhere else in 5e that I'm aware of. Mainly because there wouldn't be a point. Concentration as a design is meant to prevent you from stacking continuing effects. Battle Hymn doesn't provide any continuing effect so it doesn't fit into the category of effects that should have concentration. There's no practical reason it should be using up your concentration. The only reason I can see is that (from what I've read) during testing it used to stay up and keep its effects active the whole time until you stopped performing or lost concentration. If that was the case, it makes perfect sense as an ability...but it doesn't do that anymore.
It really feels like that one thing was changed for balance reasons (and that sounds like the right thing to do, that sounds absurdly powerful), but the minimum was done to fix it, when it needed to be entirely overhauled to make any sense anymore.
Even if you ignore the weird design, you can still cast a non-concentration spell, activate a normal bardic inspiration (or just dual wield a weapon or cast a bonus action spell) AND still use an effect from the list every round. Which is strictly better.
It does mean bad if it breaks rules that were in place for a reason. Rule number 1 of designing things for 5e is: Do not allow anyone to do anything that has a combat effect without using an action of some kind (action, bonus action, reaction). It is a major balancing factor and it breaks that rule.
It has no saving throw of any kind for putting negative effects on people. That rule is a huge balancing factor of 5e as well. The o5e Bard can use a Bardic Inspiration to give an enemy a penalty to ONE attack roll. There's an
Plus, consistency lets people intuitively understand things. This ability is extremely confusing. For instance, every spell, ability, and class feature in 5e follows the same formula: Use an action(actions and bonus actions on your turn before or after your movement, reactions on other's turns in reaction to a specific trigger) to activate an ability, choose a target, see if that ability affects the target (attack roll, saving throw, or rarely no defense), then apply the effects. People get used to this idea and it helps them to understand the game. Battle Hymn is activated only at the beginning of your turn for free then appears to be able to be targeted at literally any time your turn or theirs in reaction to anything(?) I guess. It might be able to interrupt things, it might not. That's not specified. Like can you apply the one that gives a penalty to saving throws after the roll has been made but before success is determined? It is confusing because it doesn't follow the standard formula and we have nothing to compare it to.
It's weird design is confusing because, for instance, Battle Hymn ends at the beginning of the turn after you target it. There's one Battle Hymn choice that lasts until the end of the combat though. Which is weird, since it can't...Battle Hymn ends at the beginning of the next round. Which either means the effect ends with it or the Battle Hymn is separate from the Battle Hymn EFFECT. Which is even more confusing. Does the effect require concentration? How long does it last?
Plus, it doesn't fit the theme. I explained this to someone else I know and their response was:
"I am playing this song for no one, lalala" "oh, now it is for YOU" aaaand it's over.
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I propose this is the right way for this ability to work:
As a bonus action, you can choose a creature within 30 feet of you to target with one of your known Battle Hymns and spend a Bardic Inspiration. It lasts until the beginning of your next turn.
I'd then change a bunch of the effects that have weird triggers to remove those so they work immediately.
However, it is unnecessary for what you have in the book based on my experience of actually running. It could be worded slightly clearer but that is not a problem with the mechanics as written.
