After you’re qualified for State and it’s still early enough you don’t need to practice nonstop, you should try to find other teams you work well with in case your sister team gets sniped by a higher ranking. Also, it’s nice to carry other teams who can really improve from such experiences.
So for your first point, that can just be from your own experience. I’ve seen a completely different picture. 574D and 574C teamed up to win the Kalahari, 6008A and 6008D teamed up to win NATM, and more recently 169A and 169Y won WPI. The fact of being able to practice with them and know your partners strengths and weaknesses is very valuable, especially in higher their competitions where everyone is very close in skill level.
For your second point you are correct in wanting to practice with other teams to get used to other teams play styles, but sometimes you just might not have a choice, sometimes your sister team is just the best choice.
For your third point, I agree, if there is a better option then yes pick someone else, but you’ll be hard pressed to find two teams that will work better together than sister teams. The ability to practice together all the time is huge. Now this doesn’t necessarily mean they’ll win, if there are better teams then they could still lose, but they will have a natural teamwork advantage.
For your fourth point, everyone can have an off day, them being a sister team doesn’t effect that.
For your fifth point, yeah change is good, but you shouldn’t not pick a sister team just because they’re a sister team, and you shouldn’t pick a sister team just because they’re a sister team. You pick whoever you think you can do the best with, sister teams just happen to have a lot going for them. Now this is under the assumption that both teams are good, and one isn’t a clawbot or pushbot, that changes things.
Teams pick each other when they know exactly what to expect, agreed. 6008 DnA (As we call them in Ohio) team up when it counts, but also get an insane amount of practice in together. At a competition, they went against 6008 BnC in finals, entirely State qualified. The 6008 program also won literally every award offered, showcasing thier spectacular program. (Thier MS teams also won the MS awards.)
They do extremely well at every event they attend, and were State finalists, only losing to 2011 CnF in Finals, who are another powerhouse alliance.
And the Google tourney champs, 448X and 6627A, collaborate all the time and have allied quite a few times before, including at states. In fact, 6627A has allied with 448X or one of their sister teams at almost every tournament this year. Working with teams you’re familiar with is a huge advantage.
There seems to be a lot of outrage when teams from the same school team up and win, but why should there be? If you want to coordinate autons or match strategies with another top team from your region, even if they’re not your sister team, nothing is stopping you. 7121E and 4411S are a great example- they’re not from the same school but they’re collaborated all season and built similar robots with a lot of concepts clearly shared between the two robots. They allied and won the FL state championship by a really comfortable margin in every single elim match.
It’s not always the right call to ally with your sister team, but very often, it is. An alliance needs to work well together, and this becomes a lot easier if the teams have worked together before. And it might not be replicable at Nationals or Worlds, but that doesn’t make it a bad idea at local tournaments, signature events, or states.