If you don't care too much about standing, you can easily finish the week over the 2300 points needed at reset to start over at 1900. As someone who doesn't care about rankings anymore there are no negatives to me setting a weak defense. As for positives, well, there's a few. By having a weak defense, you drop in rankings faster allowing you to generally face weaker teams when the list refreshes. Trust me it used to get boring at the top fighting the same teams back in the day. Now with relics....that's a whole other debate now is it ☺?
Anyway back to the point. If you don't stay in the top I find the teams are more varied. And if you're able to stay on the top 250 early in the week you're still getting your 12 IC per match. (As long as you're already over 2300 points I believe. I could be wrong on that last part. It's been a long time since I really bothered with this arena crap.)
And finally the more people are on board, the better chance guys like me who are really busy in real life have at actually reaching 300 victories.
All that being said, if you have a competitive streak, I can definitely understand fielding a strong team. Odds are I'll defeat that team anyway, it'll just take me longer and give more times to the bugs to sabotage each match 😂. Plus when I'm on my tractor in the field it's a lot easier to fight an easy team than a souped up one 😁.
So there's no right answer, it depends on what you are trying to achieve. If rankings don't matter to you though, maybe fielding a weak team is something to think about. I usually have a weak defense until I reach my target then I set a better one to hold on to a decent ranking at the end.
Cheers and good luck out there.