Random thoughts:
The last Otter to roll of the production line was in 1967. Given the aging of these aircraft, more problems are in store for the future. There must be modern STOL aircraft on the market to replace these antiques, and hopefully Cayman Airways is exploring this (or not).
I've been flying back and forth between GC and LC for 25 years and not once have I been charged for my overweight luggage. They always weigh the carry on as well as checked and in the past, they weighed the passengers as well. I don't think that there is a relationship between a client's bag weight and whether or not it gets left behind. It seems the variables are how full the flights are and time of day. If you are on the last flight out and it's full, you may not see your bags for a day or two.
I have been the victim of many Cayman Airways delays, cancellations and related frustrations over the years. Now, I always book a long layover to compensate.
On the way back to GC, I always send a heavy bag ahead the day before to try to avoid having stuff left behind on LC. Never had a problem finding these bags on arrival to GC. Also, if they are threatening to leave your bag behind, the argument that you sent half your luggage the day before seems to help get your bags on the flight with you. An advantage of also flying Cayman Airways from GC to US is that you can then check your bags through in LC and not have to worry about them again.
Getting from GC to LC is a PITA but the diving is so good that I continue to go.