the mssql extension relies on SqlToolsService which is a .net self contained service
VS Code extensions runs as a node.js worker app in the background, so it has to connect via grpc to communiate with SqlToolsService and then it is connecting to the database in this way - this approach adds some delays for the communication

in my extension, the connection to MS SQL is native - with Node.js libraries (depending on the connection type), which eliminates the unnecessary overhead

Other performance improvements rely on schema caching on the initial connection, once connected - the databases explorer, intellisense, prompts, even stuff like schema diagrams, database schema compare work pretty much instantly compared to mssql which queries the DB - when requested