The money promised for the NHS was provided and much more besides by the PM who took over from David Cameron, this was Theresa May. So that was one promise met. The failure to control immigration was a political decision by the Johnson government and not a consequence of Brexit. The much talked about Dublin Convention which theoretically meant the UK could return illegal immigrants to other EU countries did not work. Overall more migrants were sent to the UK than were deported.
Whether things are better or not is a very big question and it depends which aspects. For the average person it hasn’t made much obvious difference one way or the other. Trade with the EU actually went up after Brexit. Many rules and regulations were scrapped which helped business and facilitated our ability to do trade deals with other countries, such as India, which the EU has so far been unable to do. We also renegotiated some deals such as with Japan and Turkey to improve them for Britain. Britain’s GDP has slowly increased since Brexit, but like everyone else took a hit during Covid. All the major EU economies have grown more slowly than UK. However we have major structural problems with the UK economy, which existed pre Brexit and so far no politician has attempted to deal with, notably poor productivity and excessive welfare spending, and a failure to invest in digitisation and infrastructure, like Germany in fact. These are not Brexit related, but the freedom of Brexit meant we could have dealt with these but no government, since the end of the 80s has tried to do so. Brexit was a process of leaving the EU. What we do now is up to the UK, we have the freedom, but politicians seem scared to take the opportunities they have. Rejoining would be economically disastrous, not least having to pay the EU contributions which could be up to £20bn a year and losing our good trade deals like that with the CPTPP. Paying the EU contributions will mean tax rises or spending cuts, that’s inevitable. We are likely to lose control of our currency, taxes, borders, finances and laws by rejoining.