question

I'll need to explain how the inverter / charger section of the EasySolar works. It is essentially a MultiPlus, so I'll refer to it as that for simplicity's sake.

It's popular to believe that the charger and the inverter are separate components. This is incorrect. It is actually more of a converter. It can only charge or invert, not both at the same time.
As you are aware, 230V AC comes out of the AC-OUT terminal of the MultiPlus.
Now, when mains (or generator) is present on the AC-IN terminal is it simply passed through to AC-OUT via a relay (known as the bypass or backfeed relay). The converter acts in battery charger mode, converts the AC to DC and controls the charge power according to the state of charge the battery is in. The AC that is present on AC-OUT is exactly what is present on AC-IN.
There are certain consumer expectations about the quality of the AC waveform being presented to their loads. 50Hz @ 230V are reasonable expectations.
Your generator can provide this quality of AC power within certain constraints. The MultiPlus actually has to qualify and accept the AC coming in before it will close the bypass relay to allow the power through, otherwise it will reject it and continue remain in inverter mode where it can assure the quality of the AC being output.
The Lister has a governor which regulates the RPM (to maintain 50Hz AC) and also fuel consumption. If the battery is low and the MultiPlus demands more charge power, the Lister will consume more fuel to maintain the correct RPM. As charge power tails off, so does fuel consumption, but RPM remains constant and so 50Hz is maintained within reason. The flywheel speed is not constant throughout a single revolution. The throb of your EasySolar will be in harmony with the downstroke of the piston. As a child, I remember the lights in the house subtly throbbing to the beat of the Lister in its shed.

A wind turbine, is at the command of the wind. The is no way to predict or maintain the RPM. There is no way to tell what frequency or Voltage the AC from it will be.
In most cases it is three phase AC, sometimes it is rectified to DC within the turbine. None of these conditions are suitable for direct consumption by common loads. Hence you cannot simply connect a wind turbine directly to a MultiPlus, it's just not designed to cope with this type of energy source. Firstly the MultiPlus would not accept the wildly fluctuating power and secondly, if it did pass it through neither you nor your loads be happy with its quality.
The AC is usually rectified to DC and put into a battery to smooth out the fluctuations in energy production. There are also AC coupled wind turbine controllers which feed back into the grid which has a similar effect to that of a battery system.
Solar power is different, but bears some similarities in its unpredictability and intensity of power. That is why an MPPT Solar charge controller is employed, just like the one inside your EasySolar.

"I connected my 400W AC wind turbine to a rectifier. The output I connected to a spare 200Ah battery"

You have created a potential explosive device as there is nothing preventing the wind turbine form over charging the first 'spare 200Ah battery'. This makes it a dangers setup that should not be replicated by anyone as is.

The setup only remines safe if the 1000ah battery is always able to consume the power being generated preventing the 200Ah battery from ever fully charging. Even if that were to remain the case you still have to account for the DC DC charger failing. In that eventuality with no load on the first 200ah battery the wind turbine would over charge the battery and that is how you have created the potential explosive device.

You must implement a way to dump any excess power going into the first battery if it becomes fully charged. With solar there is no requirement to consume the power being created but few micro wind turbines are safe to just unload so you need a load to divert the wind turbine to.

The other clear issue with this setup is the 200AH battery is going to see heavy cycling and or a prolonged time at a discharged state of charge. When there is no wind available the battery will be left discharged until the wind picks up to charge it again. This is an ideal way to kill the battery in a very short time.

All issues can be addresses and make this type of dual battery setup safe. A lead carbon battery is a better choice of battery in place of your 200AH battery. This is due to their characteristics as they are a essentially a hybrid battery / capacitor. They take on charge faster than a standard lead acid and can cope with prolonged time at a lower state of charge.

To address the issue of directly connecting the wind turbine to the battery with no over charge dup load capability you can get a https://flexcharge.com or make a controller using Јоhn Daniel's design https://youtu.be/RbUXmZwfYK8 or a variant of the same kind of setup.

Of cause the more regulated voltage of the second controller option means you do not even need a two battery setup but there can still be some advantages to having that kind of setup especially if using a lead carbon.