To say nothing of the fact that your stats imply that you can carry 20 nuclear shells, each more powerful than a Davy Crockett-M, in the same tonnage as a single Davy Crockett-Ms carried by an Arrow IV or Long Tom...
Well, yes. Whether you make them 50kg or 5 tons, nukes are always going to do outsize damage for their mass. The Davy Crockett-M is hardly balanced by its full-up weight. After all, except for the risk of killing its launch unit, a Davy Crockett-M is far more dangerous than any other weapon on the battlefield. If you replace the Crockett physics package with an Alamo or Santa Ana, the major difference is how much further the ashes fly.
And BT's spacecraft really make the Thumper a silly weapon. 10.5km/6 miles range of a Thumper? An aerospace fighter or other spacecraft should be able to drop a nuke anywhere on the planet ("The bomber always gets through"). Even the Cold War US and USSR knew to ban fractional orbital bombardment systems because they were so effective.
In the end, the Grand Titan's Thumper is just a short-ranged, slow-firing imitation of the Swedish Bandkanon (15 nuclear shells in 45 seconds): a giant kick-me sign for the other guy's nukes.