Until the block rewards subsidy goes away, an empty block still technically has one transaction: the coinbase which distributes the generated coins from the block reward.
So, while it isn't adding any value by including other transactions, it does, indeed technically fit the definition of mining.
Every single definition of mining states "transactions", plural. Nothing is confirmed in an empty block, it does not meet the definition. Seems to me the empty block thing is a huge oversight, and that empty blocks should not be valid and the network should reject them. The only block that should have been considered valid with a single transaction generating coins was the genesis block.
I read the usage of the plural transactions to be a set from one to many. I also think that empty blocks do indeed serve a purpose if there are no other transactions to be processed. However, I am in complete agreement that if there are transactions to be processed, any created block should include any/all of those transactions and not ignore them outright just for the sake of adding a block to the chain, or keeping miners from stale shares, or whatever else has been given as a reason.
The kind of validation you're proposing would be rather daunting. It would require every node have knowledge that when the block they're verifying was created there were in fact transactions that could have been included into that block. You can't just blindly reject all blocks with only a single coinbase transaction, because it could very well be that there really were no transactions to include (albeit extremely unlikely).