No more punitive than imposing such restrictions earlier on India's neighbours. Also no more punitive than keeping businesses and services closed for defined periods to make sure that each step of easing doesn't have a negative impact on infection rates.
But it is more punitive that what we require of those people in the U.K. who have contracted a
confirmed case of Covid (including the Delta variant) domestically. When the way we treat foreign arrivals is much harsher than the way we treat domestic confirmed cases, something is very wrong, and I would suggest it is more about xenophobia than virus control.
Also, why is India even still on the Red List? If this were truly a response to exceptional risk, India’s cases are lower than many Amber countries now (their stats may be dodgy, but so are many other Amber countries), and the VoC is well established here so importation is no longer a concern.
Slowing the outbreak by 2 - 4 weeks might not sound a lot, but remember we are extending out measures by 4 weeks to allow for the vaccination programme to cover as many people as possible. If we'd been able to delay 'Delta' by a couple of weeks, then we may not now be in the position we are now.
Even if we accepted the premise that it may have averted this delay (I agree it’s credible), hotel quarantine is an absolute travel ban in all but name (to anyone without a spare £2k, and 10 days losing income unless they can work remotely, and eating inedible food). I’m not sure that’s a proportionate response, and faced with the choice I think I’d choose the Step 4 delay. (Though as above, I think there’s a strong argument that the delay is the result of over-caution).
If you travel from India to almost all countries in the EU (let’s take the Netherlands as an example), you will (to this day) be subjected to
less than Amber-style quarantine measures. If you travel to Canada, one of the very few other western countries with hotel quarantine, you only have to stay for three days while awaiting a PCR test result. Why do we demand ten? I struggle to name any other non-Covid-zero western countries with hotel quarantine restrictions (Ireland are obviously heavily influenced by us).
Why are those lesser restrictions considered adequate for other countries, and why is Delta growing slower there despite those looser restrictions? I suggest the answer is that the U.K. has stronger links to India. I’m not sure the right way to respond to that “problem” is to impose draconian measures and to try and cut off those links.