I used to be the same - the starter would be overleveled, and I'd be screwed if it ever fainted and I had other Pokemon. But around the Hoenn games is then I started to create a good balance in my team.
When I design a team, i find out what the Champion will use. My team will be made to counter the Champion, but also be able to take down the Elite Four.
When I design a team, i find out what the Champion will use. My team will be made to counter the Champion, but also be able to take down the Elite Four.