//...the reason our economy has so many vacancies is because migration has dropped significantly//
That doesn't really stack up, though. First of all this:
https://www.gov.uk/government/statistics/immigration-statistics-year-ending-march-2022/summary-of-latest-statistics
"2.1 Work
There were 277,069 work-related visas granted in the year ending March 2022 (including dependants). This was a 129% increase on the year ending March 2021 and is 50% higher than in the year ending March 2020."
I accept that the figures for 2021 and 2020 were obviously skewed by Covid, so the comparison with those years is not particularly useful. But the figure of 277k work visas is considerably higher than the last non-covid year (2019) when 192k were issued:
https://www.statista.com/statistics/293236/work-related-visa-in-the-united-kingdom/
The idea that the workforce has been severely depleted because of EU citizens (who did not require visas pre-Brexit) returning home is similarly flawed because the numbers doing so were quite low. Over 6m EU citizens applied for "settled status" to remain her post-Brexit.
You can argue the figures incessantly but the plain fact is that hundreds of thousands of people are arriving here to work when there are literally millions of people who are able to work but are not doing so. That is an unsustainable model and no country will prosper whilst that continues. The country cannot continue to ship in vast numbers of people to do the work that those already here will not do. If, as you suggest, such work doesn't pay for UK citizens, how does it pay for those from overseas, who have just the same living expenses? You cannot suggest on one hand that "work does not pay" but on the other that there are vacancies because migration has fallen.
The UK government has decided that it will not allow low-skilled, low paid people to settle here. Whether you agree with that decision or not, it's a decision that should rightly be taken by the UK government and it should not be bound in such an important matter by EU diktats. There are plenty of people already here who can do such work. What the government must do is to make sure that those people actually work for a living. Work will very easily pay when the alternative is no income.