How have you been? I think you are overthinking teambuilding.
I reccomend condensing teamslots, so you can have more room to cover threats and make the team all around solid. This also helps purge redundant pokemon or dead weight pokemon.
Focus less on covering threats, and focus on making a strong strategy and making your opponent weak to your team first. That is one way you get good team matchups.
Ok, you may be weak to something and can't help it sometimes. Although its okay, because your opponent is weak to you. You can play around weaknesses, as some aren't worth fixing.
I usually do that, then worry about threats afterwards. Then adjust accordingly.
Trial and error is my favorite way of teambuilding. When you become good at it, you build multiple teams in one night like me. :)