TYPO3 Core

I think the issue lies with both getValueAttribute and getValueFromSubmittedFormData of \TYPO3\CMS\Fluid\ViewHelpers\Form\AbstractFormFieldViewHelper.

Here is the excerpt of getValueAttribute, with getValueFromSubmittedFormData being very similar:

    /**
     * Returns the current value of this Form ViewHelper and converts it to an identifier string in case it's an object
     * The value is determined as follows:
     * * If property mapping errors occurred and the form is re-displayed, the *last submitted* value is returned
     * * Else the bound property is returned (only in objectAccessor-mode)
     * * As fallback the "value" argument of this ViewHelper is used
     *
     * Note: This method should *not* be used for form elements that must not change the value attribute, e.g. (radio) buttons and checkboxes.
     *
     * @return mixed Value
     */
    protected function getValueAttribute()
    {
        $value = null;

        if ($this->respectSubmittedDataValue) {
            $value = $this->getValueFromSubmittedFormData($value);
        } elseif ($this->hasArgument('value')) {
            $value = $this->arguments['value'];
        } elseif ($this->isObjectAccessorMode()) {
            $value = $this->getPropertyValue();
        }

        $value = $this->convertToPlainValue($value);
        return $value;
    }

1. Previously submitted value
2. Mapped value through assigned object
3. Value attribute

EDIT:
Just switching the order doesn't fix this tho, as the check isObjectAccessorMode always returns true when the name of a form is set:

/**
 * Internal method which checks if we should evaluate a domain object or just output arguments['name'] and arguments['value']
 *
 * @return bool TRUE if we should evaluate the domain object, FALSE otherwise.
 */
protected function isObjectAccessorMode() {
    return $this->hasArgument('property') && $this->renderingContext->getViewHelperVariableContainer()->exists(
        \TYPO3\CMS\Fluid\ViewHelpers\FormViewHelper::class,
        'formObjectName'
    );
}

Despite the description, it never actually checks whether an object has been assigned. So it should actually check for the formObject and not the formObjectName, at least in this case...

The value attribute seems to still override the assigned property in 11.5 and 12.4 :/
I don't see a usecase for that order but would love to have it the other way around, so i can easily set a default value in fluid without having a lot of conditions or php code