```python
from typing import *
from collections import *

def vet_upgrade_path(installed: str, steps: list) -> str:
    """
    Vet a device's proposed firmware upgrade path and report the final tag.
    
    Args:
    installed (str): The current firmware tag of the device.
    steps (list): A list of upgrade steps, each represented as a dictionary with keys 'tag' and 'requires'.
    
    Returns:
    str: The firmware tag carried after the final step, or the installed tag if the path is empty.
    
    Raises:
    ValueError: If a step's tag is not a valid firmware tag or does not meet the upgrade criteria.
    """
    def is_valid_tag(tag: str) -> bool:
        parts = tag.split('.')
        if len(parts) != 2:
            return False
        if not all(part.isdigit() for part in parts):
            return False
        if int(parts[0]) < 0 or int(parts[1]) < 0:
            return False
        if parts[0] == '0' and parts[1] != '0':
            return False
        return True

    if not isinstance(steps, list):
        raise ValueError("steps must be a list of upgrade steps.")
    
    for step in steps:
        if not isinstance(step, dict) or 'tag' not in step or 'requires' not in step:
            raise ValueError("Each step must be a dictionary with keys 'tag' and 'requires'.")
        
        if not is_valid_tag(step['tag']):
            raise ValueError(f"Invalid tag '{step['tag']}' in step.")
        
        if not is_valid_tag(step['requires']):
            raise ValueError(f"Invalid requires tag '{step['requires']}' in step.")
        
        if int(step['tag'].split('.')[0]) >= int(step['requires'].split('.')[0]):
            raise ValueError(f"Step {step['tag']} requires at least {step['requires']}.")
        
        if int(step['tag'].split('.')[1]) <= int(step['requires'].split('.')[1]):
            raise ValueError(f"Step {step['tag']} is not an upgrade from {step['requires']}.")
    
    carried = installed
    for step in steps:
        carried = step["tag"]
    return carried
```