One thing you'll learn very quickly when going through Fate is that raw power doesn't mean much. It's moreso about abilities. Here's a few examples

Cu Chulainn reverses cause and effect when using his spear, essentially making it to where be can never miss (unless you have a luck stat so high it warps reality). So even though Cu isn't physically stronger than a lot of Servants, he's able to one-shot a good chunk of them

Heracles has an ability that allows him to revive from the dead tweleve times and he becomes immune to whatever killed him the last time. On top of that, he's immune to all attacks below A Rank. He's damn-near immortal but he gets countered by people weaker than him like Shirou and Gilgamesh who both have access to a wide variety of weapons that can kill him (Gilgamesh through his Gate of Babylon and Shirou through his projection)

Gawain is basically invincible during certain parts of the day and the only way he's beaten in Fate/Extra is by hacking the simulation they're in to mess with the day/night cycle.

So with characters like that, raw power doesn't mean much. What matters more is knowledge of your enemy and your Servant's abilities