It's not a "theoretical" tax credit. Here's the application form: https://lidp.mta.info/
Congesting pricing has dual goals of reducing congestion and funding the MTA. Low-income drivers get a break on the charge, so they fund the MTA a little less than other drivers, but they're still less likely to drive than they were before, because it costs more now.
If nobody is inconveniences, then there would be no change.
It is reasonable to say that it achieved its stated goals. Its not accurate to say nobody is experience higher costs or prevented from doing what they want.
Congesting pricing has dual goals of reducing congestion and funding the MTA. Low-income drivers get a break on the charge, so they fund the MTA a little less than other drivers, but they're still less likely to drive than they were before, because it costs more now.