That's only when comparing the first and last years though, until the new rules come into force in 2020 you would be gradually worse off in the intervening years - using their example:
2016/17: £840 tax bill [100% relief on mortgage payments]
2017/18: £1200 tax bill [75% relief on mortgage payments]
2018/19: £1560 tax bill [50% relief on mortgage payments]
2019/20: £1920 tax bill [25% relief on mortgage payments]
2020/20: £840 tax bill [20% tax credit on mortgage payments]
So under the old system where you paid a total of £4,200 for the 5 year period, with the current and new rules you pay £6,360 which is an additional £2,160 in tax.
The table on that page shows that as the percentage relief on mortgage payments drops from 100-75-50-25-0, so the proportion of interest qualifying for tax credit increases 0-25-50-75-100, the two balancing each other out for basic rate taxpayers, as they always add up to 100%. As long as the basic rate tax payer remains a basic rate tax payer, he or she should be no better or no worse off during the process.
I'm not trying to defend the change, just understand its implications for me and plan how to deal with them. I've got it wrong in that I'm still a higher rate taxpayer this year (17/18), so it will impact on me slightly. However, retirement beckons and I will be a basic rate payer next year.