Sorry, I'm a few weeks late to the party; work has been destroying me. Wanted to chime in as the Hercules is a favorite of mine, though.
As an aside, the ANV-3M is not a 'total failure.' It's kind of bad, but it's playable. FWL has worse. Far worse. And the ANV-3R on the other hand is one of our best machines in its mission role.
The Hercules is one of our best overall machines, however. For a relatively low BV cost, you get a mobile attacker that can put up a passable fight at any range. It can go tank hunting or VTOL hunting with the LB AC. The Medium Pulse laser gives it something for dealing with faster units. It is by no means great at any of these roles, but it has something for almost any occasion. Combine this with passable armor and 5/8 movement, and you have basically a more mobile Albatross. It definitely should be one of the first things you consider in a FWL force (This doesn't mean every FWL force needs a Hercules, but you should ask "what reasons do I have for not fielding one"). While the Hercules will never be a star player that strikes fear into opponents, it will immediately cover several tasks in a single Mech. From there, you can build the rest of the team as you like.
The Ultra AC refits teased in the recent TRO books seem like they miss the point of the unit, and I do not expect to like them terribly much. If you want a mobile 'big AC gun' platform, we have the Shockwave and its RAC/5. Admittedly not quite functionally identical, but close enough in my experience.