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Need to look at the SP delegated to the bots, including the aggregate. If that is shrinking then the bots are shrinking. The number of bots doesn't matter that much. The total amount paid to bots is a useful metric but it combines size of the influence (SP used for voting) with ROI, so it is a bit less clear.

I agree, delegations over time would be an interesting indicator and I'll have a look at surfacing this data. From what I remember, the SteemSQL table for delegations is tricky to organise but perhaps I can call on some help. Thanks.