I run titanium heaters that have no built in control. I'm from the belief that too much is just enough so I over size my heaters and use an external controller. Been doing it that way for years with no problems. Many different ways to reef
People don't wear seatbelts for years with "no problems"... It would be a fallacy to equate that with safe or logical in context to the probability of injury or death. Whistling past the graveyard, broken clocks, dumb luck, etc.
The fact that your heaters have no built in control and are redundant AND oversized quadruples your probability of cooking your tank.
-In your "redundant" setup the redundant part is the least likely to fail. Heaters without thermostats are extremely unlikely to fail. Titanium envelopes further decrease the probability. Keeping their heads dry (the part where the cord goes in) equates to almost no probability of failure (easily a decade or more until the heating elements will fail due to thermal cycling.
-given they are both the same age, titanium and headless and run in parallel (heating on the same cycle) chances are they will both fail at or close to the same time (heating elements thermal cycling).
-The controller is the most likely point of failure in this setup - either due to power surges or temp probe failure. The failure mode of the temp probe is almost certainly LOW not HIGH, resulting in your dual oversized heaters cooking your tank very quickly.
If you want meaningful redundancy, tghen you would be better off with two controllers with 1 properly sized heater per controller. We can debate if each heater should be able to run the tank by itself of some 60% of the load. We would use math (time to overheat vs underheat with 1 heater) to determine the safest and most applicable setup.
Again, there is absolutely zero reason or logic to have an oversized heater. All that you are doing is ensuring that if there is a fail-on situation, that the tank quickly cooks.
Oversized heaters are also prone to overshoot (even if run by a PID).
I could go on, but yes there are many different ways of reef. Not all of them logical, smart or recommended.