Does Bitcoin Core accepts uncompressed address generation? So one priv key express uncompressed and compressed pub key.

Does the latest Bitcoin Core client accepts importing it to express uncompressed address? or it automatically express compressed address?

I have not noticed related parameter for compression options in getnewaddress and importprivkey.

Is this because compressed addresses helps reduce transaction size?
You can import an old uncompressed key. It'll work fine.  Getnewaddress always uses scripts with 'compressed' keys now.  BIP-143 (segwit) style inputs also require compression.

The smaller key format results in smaller transactions, and where it's required and not just optional also simpler code.