FrogReaver
As long as i get to be the frog
I'm going to break this down into 2 parts. 1 about conceptually and the other about power.Every day I get closer and closer to just posting my bard re-tune before having playtested it extensively lol
I do generally feel like this "conceptual" idea is what most people will land on, but it ignored the sheer omnipresence, power creep, and lack of actual meaningful choice that is introduced on a holistic interpretation of the class.
Saying it's "like" something else doesn't really address an issue either. Spellcasting, in general, relies on things like line-of-sight or at least line-of-effect. Hymns ignore this entirely by being essentially omnipresent. They are able to be benefited from simply by being perceived. In fact, nowhere in the rules does it say YOU as the caster of the hymn, have to be directly aware of a target. This is a HUGE boon with the 60 foot radius size they have, essentially allowing them to cover every map that isn't untenably enormous. Bards are capable of changing their hymns at the end of ANY creature's turn as a reaction, essentially allowing them to constantly have the perfect counter for anything that comes their way. As non-frontliners Bards rarely use their reactions anyway so this is always valuable.
Unlike spellcasting, Hymns have a universal cost of 1 bardic inspiration. To even compare these effects to a 5th level spell should be obviously ridiculous. We would never say "It should be expected that sorcerers get a bit stronger" if suddenly they can cast Warrior's Instinct on an entire party for a first level spell slot simply because they reached level 11. I totally agree with you that each ability individually doesn't feel TOO bad, especially if you look at it in the context of "Well Bards get powerful spells like Dominate Monster and can even take from other classes", so it really is the granular buildup that causes problems.
Let me paint a picture:
As a level 11 bard, I can choose to make it so that my entire party has a +5 to all saving throws, essentially nerfing all the threat of an adult dragon's most powerful attack unanimously. I can keep this up essentially all combat. I have advantage on all concentration saving throws, so no worries on failing those as long as I don't have terrible CON. Further, WHILE all of this is going, I can blast a massive area with Cone of Cold and do crippling damage. All of this is done on turn 1 and I still have my bonus action AND reaction.
OR, how about:
As a level 9 bard, I can, at the start of my turn, heal a dying party member for 1d10 health, get them back on their feet, and then turn them AND an ally into Giant Apes with one single polymorph spell. At the end of their turn I can use a reaction to buff one of those apes to rolling +1 damage dice, all while I wait for my next turn to come around where I can now cast spells, sustain concentration, and move my hymns around.
Lastly, and I DO genuinely think this is important, the bard feels like it's been stripped of its identity a bit. This is something that my party's bard has echoed a lot, which is that at no point in the "level track" does it feel like his bard really emphasizes the "jack of all trades" that is so archetypal of bards as a whole, but rather it just feels like they're given all of their choices at a very low level, and levelling up is just a process of taking limiters off. This makes them more powerful, yes, but it also means choices are being taken AWAY from them. Instead of focusing on playing that tactician role, it's just "naughty word it, flip on every switch at once, and do it for 5 rounds without a pause". It really pigeon-holed the type of playstyle that my party's bard could pursue, partially because I had to start planning encounters AROUND how omnipresent these abilities were, but also because it felt like the bard, by virtue of merely existing, was seen as a passive buff to the entire party, and thus it became expected of them to perform that role.
Anyway, that's my two cents. Like I mentioned in the beginning, I ended up writing an entire re-tune to the core class, revamping all the battle hymns and arts entirely. Still haven't playtested yet, but I might end up making a post about it in the future if it works well with my party. I do totally recognize that individually everything reads a "okay", but it is these granular interactions where the friction can consistently grind things to a halt, and that's really the issue. No one cares if a PC CAN pull off really broken and cool things if they play their cards right, but this isn't that. This is just the game handing you a whole deck, telling you that you can only play one ace at a time, and then as you level up being able to play more aces every single turn all at once
Conceptually for me hymns reinforce the bard as performer, which for me is the #1 most important thing about the bard. Yes they dabble and thus jack of all trades conception as well, but they are performers first. Maybe your conception of bard is different but that's mine or you view the dabbling as more important than the performing. But for me the hymns reinforce the Bard as performer conception.
On power - the only truly game changing ones are the ones that effect the whole party and even then they are no more game changing than a Paladins Aura, hypnotic pattern, a sorcerers twinned polymorph, etc. In fact, there's many times where there are a number of spells on the bard list i'd much rather cast than use the hymns.
A few scenarios -
Mostly melee enemies start 60+ ft away from the party. Use Plant Growth and whittle them down with ranged attacks as you fall back each turn. The most a 30ft move speed creature can travel in the plantgrowth a turn is 15ft when dashing. It will take them about 4 turns to get through, in which case the party can also have increased the distance between them to 120 ft. (I guess technically you can use plant growth and a hymn, but in this scenario that would be pointless).
Any encounter where there is 1 enemy with some harmful save based effects. Tasha's Hideous Laughter (excluding enemies having legendary resistance). It's actually better to disable a foe with dangerous aoe effects than it is to simply boost the parties saves.
Obviously there are scenarios where I would use the hymns over a spell, but optimal play should have you using a good mixture of both.
Honestly, most of the rest of the post comes across as trying to magnify every little thing into a mountain of an issue when it isn't.