I like the idea of having support mobs and sentries but these are just way too weak. Here's some ways to fix it:
-Give each of them unique uses and abilities. Witches could debuff opponents and buff your team with potions, skeleton could knock players back with its bow, zombie could give massive slowness and nausea while dealing lots of damage, spiders could shoot poison fangs (arrows) to whittle opponents, irongolems could throw them around, villagers could build fortifications around your egg, etc. They need to be fun AND useful.
-Give them a nice amount of health, and make it so they can't be cheesed. Ex. Zombie can't be shot.
-Let them respawn if you still have your egg, and die when it dies.