Your 20-30mb of games is taking up 100% of the diskspace or do you mean the games are utilizing the disk at 100%.
Drives only really have two speeds: Busy and 'doing nothing'. They don't work or spin slower because you don't need the files as quickly so if you see something like 70% usage then that just means 30% of the time, the drive was doing nothing. So yeah, if your game is constantly reading from the drive, like an open world game, the 100% is completely normal. If your drive cannot keep up with the work then you might consider upgrading to an SSD.