How, exactly, is having 2 transmitters a poorly designed backup for monitoring your tank level? I use 2 transmitters and 2 AI computers that each see both transmitters. If either a transmitter or a computer were to fail, I’m good and have no need to end my dive as would be the case if I had no backup.^That^
The first problem with having two transmitters is your backup system is poorly designed. The second problem is that if you're OK with continuing your dive on the one backup transmitter, then you should have been OK with diving on one single transmitter in the first place. So it's also overdesigned.
Is it overkill? Maybe, but I had a Perdix AI and then bought a Teric and decided a backup is good to have as my diving is usually done in week long dive trips or live aboards. Life is too short to have to cut dives short or sit out dives due to possible computer or air monitoring issues. My setup avoids those concerns and works for me - dive as you like, but don’t preach your views to rest of us as fact.
I also don’t get how you can say continuing a dive on the backup means you didn’t need the backup in the first place?? That makes no sense - the backup means you don’t have to call the dive short if the primary fails - only in the highly unlikely event the backup also failed would you call a dive.