Not necessarily. Plenty of offroad guys use shielded bearings and normally clean their bearings (or chuck em after a few runs). Many onroad guys run on dirty tracks and never clean their bearings.

Metal shields are typically cheaper and easier to clean. I have typically been buying tubes of shielded bearings. I only clean them ever so often whenever there is noticeable garbage in them, but chuck em after about a year - or keep them as "give aways" to someone in the pits.

I hate cleaning rubber seal bearings, and often just chuck em if there is noticeable garbage inside.

At the end of the day, the difference in price is minimal between the two.