First of all,
t3esCNwwmcyc8i9qQfyTbYhTqmYXZ9AwK3X is not BITMAIN’s address, it’s Zcash Co.'s address for the Founder’s Reward.
And second,
t1ZYZS6ynUDbvht7vH3dMiM3rsAJ1p6EGWC is 2 years old and has mined 2442 blocks.
Now you can’t judge its hashrate just by how many block it mined. You have to know how frequently it finds a block. Recently the address mined 20 blocks for 7 days. Let’s do the math.
7 days = (2.5 min per block) * 4 * 6 * 24 hours * days = 4032 blocks.
That means it had about 0.5% (= 20 / 4032) of the network hashrate last week.
Off the topic, but personally I’m really disappointed at the fact that this youtuber doesn’t know the difference between normal mining pool addresses and the Founder’s Reward address. It literally said that it got only 2.5 ZEC on every mining reward transaction. And he gets to be a Crypto Channel, a voice of the community and a trustworthy source for the debate? Such a shame.
Edit: I’ve been tracking BITMAIN’s private pool for quite a time. You can check it here.
https://forum.zcashcommunity.com/t/flypool-bitfly-miner-centralization/
And t1ZYZS6ynUDbvht7vH3dMiM3rsAJ1p6EGWC mined only 48 blocks last month, and it’s been around since the block 0. I’m guessing BITMAIN’s GPU mining pool address.