I'm not sure I would describe them as big downsides but AWS does have advantages in some areas. RDS - Amazon's database service supports more database engines;

I'm not sure I would describe them as big downsides but AWS does have advantages in some areas. RDS - Amazon's database service supports more database engines; MySQL, MariaDB, PostgreSQL, MSSQL and Oracle are all available. GCP has Cloud SQL but it only supports MySQL and PostgreSQL at the moment. I'm sure that will change. RDS also has some advantages around getting your data in from an external server. AWS also has more services making it easier to get up and running quickly. Whether that's a good thing or not is down to personal preference. Those services tie you into AWS pretty heavily. That's fine providing you are comfortable with it. Google are more focused around open standards.