Fabric ETL

Hi we are handling migration from a client but they want to keep the inhouse ETL that generates TSQL. So this would just point the JDBC driver at the Fabric warehouse. I tried to explain that Fabric TSQL is not SQL server TSQL.

They rely heavily on temp tables, cursors, and MERGE statements that either aren't supported or perform terribly in the Warehouse engine. JDBC inserts are also going to be expensive.

They are also misunderstanding/underestimating Lakehouse. Correct me if I am wrong but this feels like a ETL bottleneck is going to happen with the migration. Should we push hard on this? Which ETLs work best for Fabric?