Knowing how PvP rank-up went down from 50 gems per rank-up to only 10 today in only a few years we all know that 2021 is the year where the max revenue event will only give 2 gem/hour.
After you take RNG into account you can turn 10 gems lottery/etc. into 1 gem/hour.
to be fair, he did mention rng based rewards like lottery and chests, etc..
I think he is talking about the current dark signer lottery and chests from drops based events.
I'm not sure it's as low as that, but after several hours of completing events and all over several days, if I do total gems obtained from farmable events/total play time I would indeed be around single digit gem/hour.