Sql Data warehouse Vs redshift Vs bigquery

I have a small question please.

I am building a data warehouse, I am always in front of a question that bothers me when is it necessary to go through solutions like bigquery from google or redshift from amazon? The answer that seems logical to me is when the data exceeds the processing capacity.

But if this is not the case, i.e., currently I’m facing a quantity of data but not huge, am I obliged to use them anyway or is view sql with scriting in python enough to answer business questions?

Thank you in advance for your answer