I have a terrible tendency to rank up anyone I'm enjoying playing in the moment. However, I'm more than aware that it isn't the best strategy, especially when pursuing more difficult content.
That said, I'd really appreciate any opinions regarding my current roster, in order to plan better for the future. Would you prioritise concentrating on a number of beneficial champions/synergies? Is there anyone here who is an absolute must for end game content?

Thanks in advance.
PS. Apologies for the scruffy editing. I got bored.