Exercise and healthy eating as a way of life are the only way to go.
Which is exactly what Slimming World is about, if you're doing it properly.
Yes there are ready meals (which have the recipes on the packet so you can make the dishes yourself if you so wish), and there are the Mugshots and the Muller Lights, but the main focus is on "speed" foods (mainly vegetables and fruit). You're supposed to fill your plate with at least one third speed, and only then add the "free" stuff (lean meat, seafood, eggs, pasta, potatoes).
There are many members of my SW group who had never cooked until they joined, and are now avid cooks. And many who never exercised, but now do. You get awards for meeting "Body Magic" targets (eg walking, dancing or cycling 20 minutes a few times a week for four weeks to start with - babysteps maybe but achievable).
You can do all of this without paying £5 a week of course, but the formula works for some people.
Some groups are definitely better than others though, and you'll click better with some than others. Have you tried going to another session with another leader and a different set of members?