Re temporary visas: spousal and family visas, which have very strict requirements, including proof of English competency, minimum income levels, proof of accommodation, high fees, and an annual NHS surcharge, are also temporary - they are even called temporary leave to remain. They last, in the first instance, 2 years and 9 months, and can then be renewed - for a fee and with lots of supporting evidence about the relationship, income, employment etc etc - for a further 2 years and 6 months. Nobody on a TLR visa has any recourse to public funds.
Only after 5 years, providing a shedload of conditions and criteria are met, can Indefinite Leave to Remain be applied for. It can take months to process. Once you have ILR, you can apply for citizenship.
It’s a painful and expensive process and not one that anyone undertakes lightly.