The bard vocation is a very weird vocation and may be hard to understand for the standard tibia player. The vocation is support and a common error in judgment might lead you to believe that they are ineffective due to the lack of visual bonuses.
I would like to start with the healing spell:
The healing spell is over time and % based. What this means is that when using this to heal a "blocker" It will always heal x% of their total health per tick. It is also aoe and thus can be used on the entire party. It may be less useful on low health players due to it being a % based heal however, it is aoe meaning its just a bonus effect. The real intention of this spell is to help the blocker heal.
Now onto anthem:
This spell is very underestimated. Do not for 1 second think that it is a spell that you should use on yourself, it is not... This spell is aoe, and thus can buff a large amount of players. It lasts for 2-3 seconds. The bard can keep this buff on a 100% uptime. This means that everyone in the range will have this buff applied for an entire fight. For every person in the fight affected by this buff its effectiveness increases. An example is on my barbarian, I attacked for 1.1-1.3 million. When my bard used anthem I started hitting for 1.4-1.7 million. That is a substantial increase in damage. Lets say that your encore does a total damage of 1 million on monsters. You would only need to buff a couple people to make up for the loss in encore damage. Each player gaining about 500k damage with the buff on, buffing 6 players would net you 3 million damage. What this means is anthem is actually dealing 3 million damage per auto attack interval. Use this buff on a ninja for example, and within 2 seconds (encore exhaust) That ninja would have dealt over 3 million bonus damage just in auto attacks in 2 seconds.
Here is the math:
Duration of attacking = 2000 ms
Ninja attack speed = 300 ms
2000 / 300 = 6.6~
Times the ninja will attack every 2 seconds = 6.6
Bonus damage yield from anthem buff = 500,000
500,000 * 6.6 = 3,300,000
Within 2 seconds of attacking the ninja will have dealt 3,300,000 bonus damage. Now use encore, see if you deal 3.3 million damage with it, you wont. Now put anthem on a party of 6. Then tell me it is useless.