I agree that DeFi yield harvesting is risky but for completely different reason. The risks are mostly to do with smart contract bugs and platforms shutting down. 

There are plenty of options for using stable coins and hedging the tokens and thus ensure that the return will not depend on the token price.

At the time of writing the weekly percentages were 0.3%, 0%, 0.2%, 0.5%, 0.9% which I did not perceive as weekly doubling. But I was likely fooled by the noise of the first weeks where numbers were too low to be meaningful. Yesterday latest weekly numbers came out and last week the percentage was 2.3%. So numbers are clearly worrying and in line with Zvi's post.

About the English strain part. This seems very one-sided to me. Only the evidence in favor of it being more infectious is being shared by Zvi.

1. In Denmark 12.5% of all positive COVID are randomly sequenced. The English strain has been observed in the samples since 14 November. However it remains stable at 0.5-1% of samples. This makes me update in the direction that it is not 70% more infectious compared to other strains. Otherwise we should see the strain make up a larger proportion of positive samples over time. (https://files.ssi.dk/engelsk_virusvariant-28122020)
2. The graph "One of these lines on that second graph is not like the others" is highly selective. You can add other European countries with a similar slope as UK where the English strain is not responsible.

The basic idea is this. Let's say you buy a bitcoin at 23k USD and sell the BTC futures contract for 25k. At expiration date (or sooner) you will get 25k but will have to handover the bitcoin you paid 23k for. No matter the spot price at that point you will still have made 2k (minus fees). If bitcoin has gone up to 30k you are giving away an asset worth 30 in return for 25k, but you still made a profit since you bought it for 23k. But be aware that the high bitcoin volatiliy can eat your margin account.