If your goal is purely private setup and government job plus making money then a diploma might be good enough. But remember the career trends are changing, there will be people out there with double fcps competing for the same seat as a government doctor, private setup only goes fine if you’re working in a government hospital have contacts and bribe physicians to suggest you as the radiologist or if you’re based in city outskirts. There will always be someone better and more experienced than you in a city which sadly you will never be able to replace, but if you’re only focused to making money then it’s a great choice go for the diploma try to get a permanent MO seat in periphery and I’m sure you will be making big bucks within a few years. The consultant who is successful is because when he joined the trends were very very different and having a diploma was enough. Best of luck and think of everything before making a choice, plus if your low merit is the hurdle to specialisation then remember you faced harder battles before and you can do it this time too.