If they just cut a hole in the rear of a trailer designed to be at 10% tongue weight and you cram a 2000lb toy at the very rear...sure that would be a big concern.
Most toy haulers (5er or TT) start out heavy in the front so when you load them up, you still have a reasonable tongue weight. That doesn't mean you can do stupid things but if TT toy haulers were death traps, they wouldn't be building them.
We recently purchased a 25ft TT Toy Hauler and there is almost nothing but box behind the axles when empty. Just the fold up couches and table (maybe 100lb). Kitchen sits over the axles, Bathroom & Bedroom with storage are all in front of the axles. Tanks are at or in front of the axles. The axles are a bit further back compared to similar TT also, so a pound added up by the bedroom will cancel out more than a pound in the garage area in terms of determining tongue weight.
We didn't weigh it empty (we do have to swing by and weight the rig soon) but according to the specs, empty is 15% tongue weight. We've seen a lot of TT that start in the 8-10% range (they assume it will increase when you load it). So if you put 400lb of personal effects in the front, that might cancel out 600lb of toy in the back, which might result in the tongue weight dropping to 12-13% loaded (you need the weights and positions of everything to do the calculations) which would generally be fine.
