Worth taking the points one at a time, because some of them rest on facts that have changed or are actually published.
On data being deliberately not collected: crime by ethnicity is published by the Ministry of Justice in the Race and the Criminal Justice System statistics, updated annually. Immigration status of offenders is patchier. So the "they won't tell us" picture is half-right.
On benefits for polygamous marriages: Polygamous marriages contracted in the UK are void. The "benefits for second wives" line is a long-running myth that does not match how the benefits rules actually work.
On cousin marriage: there is no benefits payment tied to cousin marriage. It is legal but not subsidised. That framing tracks racialised assumptions more than actual benefits rules.
On low-paid migrants bringing dependents: that picture mostly describes the pre-April-2024 system. The Skilled Worker salary threshold rose to £38,700 last year, and dependent visas for care workers were restricted in March 2024. The lever you describe has already moved, and the article touches on why net migration is now falling.
On a labour market test: UK had the Resident Labour Market Test until 2020. The Johnson government abolished it when it brought in the points-based system. Restoring something like it would be a return to recent UK practice, not a new Australian import.
On NHS waiting lists: the "removed from lists" concern is partly real. NHS does remove patients who decline two appointments without rebooking. But the headline wait-time movements can be cross-checked against the NHS England monthly RTT data, which is published in granular form.
On the broader instinct that you want harder numbers and clearer trade-offs from government, that is reasonable. Some of the fixes are available in the published tables if you know where to look. Some are genuine collection gaps. The myths in circulation make it harder to tell which is which.