Frozen veggies meets gumbo = flavorless. How to add flavor?

So, last time I made gumbo, I got the veggies chopped (onion, celery, green pepper, and garlic) and then realized I had prepped twice as much as I needed.

I froze the extra ingredients, labeled for future use for gumbo.

I’m making it again now, and it’s pretty flavorless. (See below for exactly what I’ve done.) Since the last time I made it was over a month ago, I don’t recall exactly whether it was this bland last time.

What might cause flavorless gumbo? Is it the frozen veggies?
Is this dish supposed to be somewhat bland? I’ve actually only had it once or twice at a restaurant.
How could/should I add more flavor to the current batch?

Process:

1. Heat 1.5 TB oil, add 1.5 TB flour to make a dark brown roux.
2. If I were using fresh veggies, I’d add them next. Instead, I held off.
3. Add 1/2 cup tomato sauce, stir until it gets crumbly & dry.
4. I then added the defrosted, drained veggies.
5. Fry 1/2 pound okra in a separate skillet until it’s less sticky & less stringy, then add to the pot.
6. Add 1 cup fresh, chopped tomatoes.
7. Slowly add 1 1/2 cups water.
8. Add 1/2 tsp sugar, some salt, pepper, and I actually also added a dash of hot pepper sauce since it was so blah-tasting.
9. Simmer for an hour.
   …. this is where I am now, and it’s just.. blah, still.
10. The next step will be to add 1/2 pound shrimp, a bay leaf, some fresh parsley, and cook for another 30 minutes.