The selfish mining strategy relies on withholding a block to build on it in private. When the honest chain publishes a block, the attacker immediately broadcasts its own withheld block in order to try to replace it.
Today, most miners are connected via FIBRE and the general network has compact blocks to exchange compressed blocks. The delay until a block is known to the complete miner community is thus much smaller than in 2013. It seems that under the "first seen paradigm" selfish mining becomes a losing strategy for blocks with such short relay times.
Is it correct to conclude that selfish mining is a theoretical attack now?