From my understanding, Umayyad Al-Andalus relied on mercenaries, mainly Berbers, for an army.
this depends on the period, during the Al-mansur era with the destruction of the Arab elite. The army was made up primarily of Berbers and Saqaliba(slavic slave soldiers). Andalus before that had a the standing army, known as the "Armis" or "Armiya" in Arabic. It was composed of both Arab and Berber soldiers, who served as the core military units. In addition to the Armis, the Umayyads also employed auxiliary forces, such as tribal warriors and local militias, to supplement their military strength. So while they used mercenaries most of the army was normal. Individuals who were enlisted or conscripted into the military and received regular training and payment from the Umayyad authorities.
They didn't really have a standing army of their own.
Under the rule of Abd al-Rahman III, it could have fielded anywhere from 30,000 to 50,000 soldiers during its peak. The issue was that the army was composed of Arabs and Berbers. Muladi soldiers, being of Iberian or Hispano-Roman origin, often faced discrimination or perceived lower social status compared to soldiers of Arab or Berber origin. This disparity in social standing could lead to a lot of friction and resentment within the military ranks. What changes with Umar is that the army will be primarily made up of muladis. What is more viable in the long term as they have the largest Islamic population
Assuming this is true, an Al-Andalus ruled by locals rather than a class of foreigners relying on other foreigners to keep the country in line could be much stronger militarily.
yes it was a vicious circle. Muladis were viewed with suspicion due to their Iberian heritage and potential ties to the local population, who were not wholly supportive of Umayyad rule. This perception of potential disloyalty could lead to their exclusion from positions of power and responsibility. Couple this with the Arab-Berber Alliances, the Socio-Cultural Differences plus Arab Supremacy and you have a recipe for the exclusion of the kingdom's largest manpower base. (It seems a bit stupid to us, but following a logic of Arab supremacy it makes sense)
At the very least without having to worry as much about internal issues Alt-Andalus would already be stronger militarily.
@Nivek will probably know better than me but all Muslims who owned land had to serve. Making room for muladis in the army (even with the losses of a purge of a good part of the Arab and Berber elite) probably significantly increases the nation's manpower.