The problem with this suggestion is that usually, players don't team for two games in a row*.
For an /sr report to be forwarded to a staff member it requires a noticeable amount of reports, this means that by the time a moderator gets alerted, the game with the teamers would probably have already ended and therefore the report is a waste of the mod's time.
Additionally, most times there won't even be enough reports in a single game for it to be forwarded (This is just an assumption, we don't actually know the number of sr reports required for a staff member to be alerted) and as I've said before, players don't usually team for two games in a row meaning the report would probably expire untill they team again.
This is not the case with blatant hackers as they don't usually stop hacking after a game (unless they are super smart and can guess when they are being watched by counting the number of volunteer staff online and assuming how many players have already reported them, but that's just a wild thought though haha)
You also suggested an option to type out the name of the rule the player is breaking. In my opinion this will create complete chaos as there will be a huge amount of troll reports and unclear reports such as different languages, spelling mistakes and unknown cheats.
To conclude, I think the sr system is great as it is and adding a teaming option and/or an 'other' option will waste the mods time and disrupt the order of the current system.
*This is because usually teamers find their teammate on the spot and for a teaming to happen there has to be two players willing to team with eachother which is not as common as it seems, and that happening for multiple games in a row can be very rare.
The exception is with irl/online friends who will probably team for more than one game.
p.s.
I'm playing on the Java edition network so if some of the things I said are not correct in Bedrock let me know (or if there are any mistakes at all).