I'm really not sure why you're asking this question. You're not going to receive a statistical appraisal of your chances, as we have no sources that could be used for such a comparison.
In a battle you are more likely to die if you are fighting and not wearing armour. You are more likely to die if you are not a member of the aristocracy (with some exceptions such as the Battle of Towton or Evesham) as there is no value in capturing you (I assume that you are talking about non-nobility by referring to 'armourless' infantry).
Here are a couple of extracts from other posts I've written on the topic which are related but not directly addressed at your question.
On arms and armour:
Arms and Armour: The equipment of the knight was incredibly expensive, a mail-shirt (hauberk) could cost the annual income from a small village and a quality warhorse could cost the same. The current consensus regarding mounted warfare was not that the equestrian class emerged with the discovery of new mounted technologies (I do not refer here to the stirrup, which emerged in the eighth-century, but the improvements of saddles, etc.) and the accepted view is that the warrior elite adapted and pursued these new technologies in warfare when they became available (Ayton, 1999, 188). We can infer that these vast sums would not have been invested in arms, armour, and horses had they not been effective. This is not to suggest that arms, armour, and horses alone created a deadly warrior but that these elements were regarded as useful by contemporaries who had some experience of warfare.
To make a brief tangent, you seem slightly obsessed with the incapacitation of the mounted warrior by a stray spear or sword into the belly of his horse. Firstly, slashing downwards gives your blow more force and your enemy's head is at much greater risk than your horse. Secondly, the risk was ameliorated by the fact you, and possibly your horse, were heavily armoured. Also, it was not until the Early Modern period that armour became so heavy that, if dismounted, you could not get up and carry on fighting. Yes battle was risky and not even the best armoured, best trained, best protected knight or king could be guaranteed to escape a battlefield alive.
On the treatment of commoners:
Chivalry was not a concept which was either aimed at or directed towards the 'commoners'. The ideas that we conflate with chivalry (protecting women, protecting the poor, the church) emerged from a series of councils organised by the clergy in Occitania in the late- tenth and eleventh-centuries. These were called the Peace of God movement and were directed against the proto-chivalric class and mostly at the proto-nobility (ie. landlords) who were often violent in the practice of their lordship and private warfare.
Chivalry was a later creation, which I discuss in the post mentioned above, but to condense: it was the emergence of a conscious code which combined a warrior ethic with a Biblical one c.1170-c.1220. This conscious code was fluid, inconsistent, and occasionally thoroughly contradictory. But it was a shared discourse across several distinct polities but between individuals who could be loosely equated. It was this social class to whom the benefits of chivalry were aimed.
On ransom:
Another attribute (loyalty) meant not solely that one should be loyal to your lord but that one should be loyal to your word. Ransom was built on mutual respect and trust as it was likely the prisoner would be released merely for a pledge (ie. promise) to pay his ransom. This was a wider part of reciprocal obligations that the martial class imposed upon themselves and would rely on one another to enforce (not that they always did, of course). There were other factors at play. The Frankish diaspora and marriage among the nobility had created a situation where male kinsmen may well face one another while serving their lord or king. It also made sense not to kill those whose kith (friends) and kin could feasibly retaliate. The rise and popularity of the tournament in the twelfth-century created not only a point where large numbers of similarly-minded individuals could test their prowess and win honour, but could test these principles and loyalty to their vows. Finally, and made most obvious by the tournament, was the economic incentive. Ransoms were far more valuable than dead nobles and knights (in most cases).
There was little or no such incentive to preserve the life of those who could not pay a ransom. There are literally dozens of famous examples of the execution of common soldiers after a battle. The modern concept of the merciful knight has intruded from the historiographical conflation of the Peace of God movement and the Romanticisation of chivalry in the eighteenth- and nineteenth-centuries. Mercy was extended usually to your peers and the rest may as well go hang.
The comments in full (with references):