@Choux
The domicile rules were reformed in 2017 so that once you have been UK tax resident for at least 15 of the last 20 tax years you can no longer claim the remittance basis, making you liable for UK tax on your worldwide income.
A charge for using the remittance basis was introduced in 2008.
So the rules are not as favourable to non-doms as they used to be.
But domicile status has been part of the tax system for 200 years and so far as I am aware no government, including a labour government, has ever seriously tried to get rid of it altogether.
Overall, keeping the remittance basis increases the UK tax take because it encourages rich people to live in the UK and therefore pay some tax here. Rich non-doms are inherently mobile and don't usually have to choose to reside in the UK and won't if it drags all of their foreign income into the UK tax net. You might disagree with it but that is the economic rationale. The UK would be very unlikely to be better off if we tried to tax non-doms on all of their worldwide income.
And also the difference between claiming the remittance basis and not is not always that significant because usually the UK gives credit for foreign tax paid before UK tax is calculated. If, for example, you have already paid 40% tax on your foreign dividends you won't usually owe extra UK tax (and as always with tax there are various exceptions to that).
To be fair, I suspect that Sunak's wife is saving a fair amount by claiming the remittance basis as my understanding is that Indian dividend rates are significantly lower than UK rates but it doesn't sound like she's doing anything which would constitute "tax avoidance". She's using the rules in exactly the way in which they are intended to be used. There may also be practical reasons not to create large UK tax liabilities such as exchange control rules in India, though I'm no expert on that i.e. could she actually get the dividends out of India to pay a UK tax bill.