Why do these types of inverters produce different output power?
I can't open your links, so this is an educated guess...

Both bridge configurations are using semiconductor devices, and can switch a heater on and off reliably for years.

A single-switch configuration, using something like a relay or contactor to interrupt power to the heater is going to fail due to contact arcing, especially at higher power levels.  Mercury relays were often used in this configuration, as they did not have the contact breakdown problem, but due to the toxicity of mercury, and difficulty of disposing, they have mostly been phased out, to be replaced with semiconductor devices.