Don't you think he just have more hashrate?
He might have more hashrate, but he mines with difficulty=1, as everybody else. Testnet4 is specifically designed to be mined with CPU, because every 20 minutes, difficulty returns to 1. It'd be understandable if he mined in ASIC difficulties, and rewrote our CPU-mined chain with his, but he enjoys the benefit of mining with ASIC on a CPU difficulty. It just drives me crazy!
Essentially, he continuously wins on block propagation every 20 minutes, because that's the only game you need to win, when difficulty is 1, and everyone can mine a block. The only reasonable explanation is that he's using a software like ckpool, which is has better optimization on block propagation, than Bitcoin Core.