There's a few things to clear up. First, a short answer to your question:
There is no 'best team'. No technically best, no practically best, nothing. An objectively best team doesn't exist and never will.
Second, in what makes a team good, you don't seem to understand the variables, of which there are many and almost all subjectively based (and the ones that are objectively based can subjectively be applied better). Type synergy exists, but so does offensive synergy. So does momentum. So does team roles like walls and wallbreaking, offensive cleaning,. etc that need to be balanced together. And then there are issues of limited coverage available within movesets and strategy. And THEN there's the whole issue with archetypes. You have offensive, hyper offensive, balanced, balanced defensive, bulky offence, stall, semi-stall, volt-turn, webs, hazard stack and weather variations of all of these. No style is objectively better than any other, and the each composition consists of so many different combinations that what's 'best' changes compared to what it goes against. You could have an awesome team but if it goes against a certain couple of Pokemon, no matter how unlikely, it will lose (assuming players of equal skill in every match using said team which won't happen but you get the point). There is no objectively based archetype, and no objectively best team composition with each archetype. Thus there is no best.
Tl;dr the amount of subjective and archetype-related choices means nothing can ever be objectively best.