"As the table shows, the answer is, mostly to the richest.
The people in the top decile receive 40% of all the pension relief, a third of the relief on the sale of domestic properties, and half of the ISA relief."
https://eastangliabylines.co.uk/business/economics/guess-who-the-tax-system-is-really-supporting/
The analysis of pension relief is highly flawed. Pensions contributions aren't taxable because pension income is taxable. If both were taxable, it would be mad for anyone to save anything into a pension fund because it would get taxed twice.
Investigating the tax treatment of pensions in payment would be worth doing. But there's no light shed on it here.