Hannibal had lost Capua and Syracuse in 212 (Sicily was under full Roman control by 210 BC) and Tarentum in 209 BC. Yes there would have some kind of impact by having the two armies combined but how big an impact? The Romans had been satisfied with limiting Hannibals power and had slowly grinded him down for nearly a decade after Cannae.

Even with a stronger army Hannibal would have needed at least one major victory (Cannae like) to have any real impact on the allies of Rome. And he would still have been outnumbered by Roman forces, even if Hasdrubal had won at Metaurus and not just slipped through the net without a fight.

The Romans were more careful and experienced compared to 218-216 BC, where Hannibal had his greatest victories. What were the chances for him to get a big victory again instead of just more years of attrition? Remember that the Romans managed to keep him down in southern Italy, his brother Mago in Gaul (who invaded with a small army in 205 BC) while still preparing for Scipio to invade Africa.

Hannibal might have been able to outwit most Roman generals to prevent being forced into battle unless he had an advantage, and occasionally lashing out and hurting a Roman army by surprise, but he was still outnumbered in hostile lands against a foe who had more resources than he had.

I dont see gaining 30K men from Hasdrubal really would have changed his position that much.

If we to trust Livy he says:
[27.36]..The total military strength amounted to twenty-three legions and were thus distributed: each of the consuls had two; four were in Spain; each of the three praetors had two in Sardinia, Sicily and Gaul respectively; C. Terentius had two in Etruria; Quintus Fulvius had two in Bruttium; Q. Claudius had two in the neighbourhood of Tarentum and the Sallentine district; C. Hostilius Tubulus had one at Capua; and two were raised in the City for home defence.
That leaves 15 legions on the Italian peninsula and another 4 close by on Sicily and Sardinia. It also appears that additional forces were sent from Spain and Sicily as well as volunteer slaves were used.


CBR