To lay it out in numbers:
BEFORE £1 pay increase: £X earnings, £Y benefits
AFTER £1 pay increase: £X + 1 earnings, £Y - 0.63 benefits
DIFFERENCE: £0.37
So a pay increase of £1 leaves you with an actual total increase of £0.37. This corresponds to an effective tax rate of £0.63.
Universal credit replaces a wide range of legacy benefits. One of the legacy benefits it replaces is "working tax credits". These were payments made to people who were working and on a low income.
This part of Universal Credit "tops up" your earnings from work. They are in addition to your earnings. is.
When someone on UC starts working they get their pay from work, and on top of that they get their their universal credit minus 63 pence per pound that they earn from work.
In the past if you did more than 16 hours of work in a week all your benefit would stop, but under UC you can work over 16 hours in a week and keep the money.
Universal Credit work allowances: https://www.gov.uk/government/publications/universal-credit-...
What the earnings taper is and how this affects Universal Credit: https://www.entitledto.co.uk/help/Earnings-taper-Universal-C...
How your earnings affect payments: https://www.gov.uk/universal-credit/how-your-earnings-affect...
Yes, it's 'valuable progress'.
That doesn't mean complaints are invalid, or "letting perfect be the enemy of good". What a rubbish accusation. You're only letting perfect be the enemy of good when you use a problem as a reason to impede the weaker solution. This is a comment hoping for better. Don't shame that!
If your response to the weak solution is to talk about how bad it is, you're setting the wrong incentives.
And beyond that you're letting perfect be the enemy of good here. Eliminating the cliffs and capping the marginal tax rate of the poor at 63% is valuable progress. If you want things to get better you should celebrate the small victories, not treat them as an opportunity to complain more.