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I think I have the answer, but I'm torn between two options.
Infantry Online
is an online game where one of the modes is sci-fi humans vs. monster alien bugs, and it's been around for a very long time. I can't say much more than that as I've only ever played it briefly.
Savage
and Savage 2
aren't really sci-fi and the beast team aren't bugs, but the beasts faction has a unit called "Behemoth" that is a giant ogre with a club. It also has different buildings that provide different things like you say, with one player acting as top-down commander. It's basically Natural Selection in a Science Fantasy setting. It looks like Savage XR
is a community spinoff game from the source code.

I remember my brother and me playing this a lot probably around 10 years ago, ish? It was online multiplayer, no voice chat, just text.
The setting was a generic grassy/rocky hill environment. The teams were humans ( I think vaguely scifi-knight ish?) vs monster-alien sorts with a bug/reptilian vibe? Nothing super unique. The classes were the standard soldier, stealth, healer, magic and I remember the monsters' big tank class being the "Behemoth": A slow moving, giant ogre with a club - tended to be used to smash buildings. I think the humans had a tank. The bases had different buildings supplying health, upgrades, weapons, classes and there was a top down build mode for one lucky player.
I think you could also play it with NP Cs and just build your base and have the computer control the enemy, whilst sending out your own units. Might have been labelled a "practice mode".
We probably would have downloaded from a website like kongregate or similar; it was it's own client, not part of website.
I don't think it was related to War Hammer but was likely trying to mimic that sort of game.