About 14 minutes between messages theory: If there is a problem, a long typed message isn't priority, and it is sent at 11:00, which would make it even more likely that it is something sent on regular basis. If there would be problems at this time, when they have time for typed messages, they would have time to decide deviate, return, etc. with many options. And if things would get worse (slowly) in the next 14 minutes we would have reasons to expect to see more communication attemtps, etc.
Why no MAYDAY or PAN-PAN message sent to ATC? We don't know the exact reasons, even if we assume they could contact ATC somehow, and the storms didn't make it impossible, their radio was working, sending such messages are urgent if you expect ATC can offer some assistance.