A friend of mine and I have been trying to beat the event [Powerful Enemies] without the suggested event support, just for the fun of the challenge. When we found "Heavy Cruiser Alpha" 350k Rider with 96% (80% x2) damage resist + AoE 100% crit rate up we thought this is impossible, especially for us non-whales/f2p.
To our surprise we managed to beat it, with the stars of the show being Serenity and Osakabehime of all servants! They managed to do what no other servant in our roster could and actually beat this ridiculous fight!
It just really goes to show that every servant in this game can have a time and a place to shine, even the super niche ones and there's something really satisfying about that.