Sry should have been clear, too low. So low it's easy to ignore
Average Londoner earns something like 40k GBP/yr. If they have to pay the congestion charge every day, that'll eat up 12.5% of their annual income.
But I agree, it'd be nice if the charge was 100GBP per day and I was the only person on the roads.
I think the hope is with the fee on an average day you don't drive and you drive only when you really need it so the proportion of income should be lower and the fee higher to compensate.