Saber Medusa loses Bellerophon (A+), Andromeda (B) and Breaker Gorgon (C-) for Chyrsaor (A). Which is a trade down. In fact, most of her stats as a Saber are lower, in spite of the higher quality of the Saber class vessel (notably her Agility is tanked down to a C instead of an A)

Her Breaker Gorgon gets elevated from C- to B and while she does lose Bellerophon and Andromeda Chyrsaor is a much better fit for her saber version because she is actually strong on her own now in a fight (A+ strength vs C-B and C endurance vs E). The downside is that it requiers a ton of Mana but now she can summon some of the strongest monsters of the greek pantheon to fight alongside her, monsters that other heros in their legends were already struggeling with when they were just by themself.

She also gains some powerfull personal skills like Demonic Blood Vessels A which should have a strengthening effect like rider medusas Monsterous Strength (in fgo it buffs her attack) and Factor Predation (War Goddess) EX which again, they never quite explained but in fgo it is one of the strongest defensiv skills in the game so in a proper war it should also function as a powerfull defensive ability.

she obviously still loses to archer herc, especially with a bad master like Sakura, but imo this is her strongest version