They were never very serious to begin with,being even in Kanto comic relief.The only episode where they seemed like serious villains was in second and third episode "Ash catches pokemon" where they were represented as some treat,though lost against Caterpie was shameful.
I suppose some people considered them more serious in early seasons because of usage of real bombs and guns in some episodes using unusual methods compared to nowdays,but despite that they were always portrayed as "someone who cant be taken seriously".
How i feel about whole thing?Well i like the way they are now with their funny antics,with Jessie becoming more competent as trainer(that would be actually incorrect,meant coordinator),but i wouldnt mind seeing their bserious side for a change being for once a treat.
Also from what i notioced when they are serious,oir having more selfconfidence(like James got at times),they can battle quiote decent.
The only real villains ever if you ask me were:Cyrus and Team Galactic,at times Butch and Cassidy(not always),Hunter J of course,Giovanni and TR organization,Team Aqua and Magma and if it counts Mewtwo.