There's still huge difference between say Gareth and Galahad.Nah, it's actually overblown how strong or weak certain Knights are(There is a difference but it's not a huge enough one for it to truly be a difference. Percival still died despite being against the traitors and wanting to stop the Lion King, Artoria can canonically beat the brakes off of every other Knight with hilarious ease if she wants and Bedivere is the weakest but he can still stomp the shit out of most Servants even before he got the Excali-Arm).
The big issue is that Kaguya... is a massive idiot who throws her power around and has base tactics and that's it. It's easy for a Knight to overwhelm her once she starts running low.
Rin just seems to do whatever she wants and Sakura just plain never wanted to be in the game at all.
Also, discounting Algertam, what does Bedi have? I mean can't see his skill is on par with say Yagyu.
Well, Rin does intially wants to succeed her father and we know her father is obsessed with Tohsaka legacy (finding the Root). And I don't consider Sakura to be a Mage tbh considering Zouken screwed her training (and body)