Whether or not a protagonist is able to overcome an antagonist or other obstacle is mostly a means to present the level at which the stakes are at in a story.
Sometimes a hero is able to easily defeat an enemy on their own without help and in other they struggle without help or completely fail, sometimes because of their opponents greater strength or because they (the protagonist) are weaker or not skilled enough.
I'm a long time Sonic fan so it's easiest to draw examples from there but there's numerous instances whether in the games, comics, or tv series where Sonic can easily dispose of a foe or opponent without issue and is known for that ability. But in other instances he is in a position where he requires the aid of his friends. There's instances where the stakes are changed and he becomes a liability in the narrative, like the arrow of flame in Secret Rings, being transformed by Dark Gaia's energy in Unleashed, or falling victim and nearly succumbing to the metal virus in the IDW comics. Frontiers I think did a good job of showing both where Sonic, having fought tons of battles up to that point, does have skill to take down certain obstacles but also has moments where he visibly struggles without the aid of his friends.
So you can have "invincible" heroes able to defeat whatever comes at them but you can also create tension or higher stakes with an opponent that the hero needs help to take down for any number of reasons; it's just a matter of what feels right for a story. Though I do think it's also worth noting the general kid's media aspect in that their trying to teach and encourage young viewers to know that "it's okay to ask for help when you can't do something alone" and other moral lessons like that. It wont always be one or the other but it's something to keep in mind at least from a viewing perspective.
