Its not set long after the Clone Wars. Like 3 years ive seen somewhere.
But we know as a fact Jedi get rusty. Like Kenobi in his first fight against Vader in his show. Though that was 10 years tbf. But it doesnt seem to take them long to get back into things - Obi-Wan was back to form 3 episodes later and even got a power boost. Maul from Revenge to Revival also comes to mind.
We also dont know of any shorter or longer term effects on Ventress from being resurrected.
Tbf, canon's always stressed that not training for some time deteriorates your skills. Think about Kenobi not doing anything for 10 years and being Vader's ***** in their first duel. Dagan Gera and Rayvis were both much weaker than in their prime after being put in stasis and in jail respectively. Even Cal Kestis, who didn't use a lightsaber in 5 years, had forgot most of his Padawan skills and was barely above Initiate level at the beginning of the game. And Barriss Offee went from pressuring S5 Anakin in sabers to being treated like fodder by the GI. Training matters in canon, so I'm sure this Ventress is nowhere near her prime