I don't think so. If the DM is creating DCs based on player level and not what DCs actually are, then yes you are correct. However, if the DM is making moderate tasks DC 15 regardless of whether the PC is level 1 or level 20, then the overwhelming majority of DCs will be in the 10-15 range. 20 will be uncommon, 25 rare, and 30 very rare.
Expertise isn't a must have for games like that, since you aren't encountering those high DCs very often unless you the player are going out of your way to try and do really hard things for some reason.