To me it always seemed that Luke mastered saber combat much earlier comparing to his Force capabilities. Between ANH and ROTJ there is big enough years gap for Luke to master saber combat through practice with droids or whatever means. Hence, during saber duel with Vader Luke was described as his equal. Later he faced Lumya and defeated her with shoto. Decades later one would assume he would be able to stomp her, yet, he still felt like he needed shoto to be able to defeat her.
Force wise even 8 years post ANH Luke was easily Force handled by Gedzerion.
So while I do believe that Luke can give a lot of trouble to Dooku, when pared with Kenobi, he is still a fodder for Dooku's Force attacks.