Do Sri Vaishnavas really believe that all names of Devatas in the Vedas are to be interpreted as directly referring to Narayana?
No, not at all.
First of all, according to Mimamsa, words should be interpreted in their primary meaning unless there is a reason otherwise. So words of Devatas like "Indra" should be interpreted as referring to the Devatas.
Also, names of Devatas can have multiple meanings as we'll soon see. The name of a Devata can refer to that Devata itself, can refer to Brahman as the Antaryami of that particular Devata, can be used as an etymological name of Brahman, or can refer to something other than Brahman and the Devata. For example, "Indra" can refer to the mind, or to the Jivatma, etc.
How we know how a word is being used is determined from the context the Vedic passage is in, as well as the Upabrhmanas (Smriti).
Itihasa puranabhyam vedam samupabrhmayet - Mahabharata (Adi Parva)
"One should interpret the Vedas with the help of the Itihasas and Puranas."
Which means that, when we come across the Vedic verse that says "Indra killed Vrtra", it is a clear reference to the Puranic story in which Indra Devata killed Vrtra, which means that "Indra" in the Vedic verse is Indra Devata.
The blog also states:
Here, we have the pramAnam from the Brahma Sutram, “Sakshadapyavirodham Jaiminih”. It is mentioned that Jaimini believes all names in mantras, despite indicating the antaryAmin of the devatAs, are also directly (sAkshAt) interpreted as referring to nArAyaNa.
Ramanujacharya's commentary on that sutra explains what Jaimini means. Jaimini nowhere says that all names in mantras directly refer to Narayana. Ramanujacharya explains Jaimini's position thus:
Jaimini, on the other hand, is of opinion that there is no reasonable objection to the term "Agni," no less than the term: "Vaisvanara," being taken directly to denote the highest Self. That is to say--in the same way as the term "Vaisvanara," although a common term, yet when qualified by attributes especially belonging to [Brahman] is known to denote the latter only as possessing the quality of ruling all men; so the word "Agni" also when appearing in connection with special attributes belonging to the highest Self denotes that Self only.
What he means is, in the Vedic text under discussion, "Agni Vaishnavara" is said to have the entire universe as his body, as well as dwell within man. Now the question is, is "Agni Vaishnavara" referring to the gastric fire in the stomach, the fire element, the fire deity, or Brahman? It cannot refer to the gastric fire, the fire element, or fire deity, because they do not have the entire universe for their body. However, it can refer to Brahman because Brahman does have the entire universe for his body.
Now the question is, is the word "Agni Vaishvanara" referring to Brahman as the Antaryami of Agni-Vaishvanara, or is it calling Brahman by the name Agni-Vaishvanara?
In a previous sutra, it was stated that the word "Agni" in the compound "Agni Vaishvanara" refers to Brahman as the Antaryami of the gastric fire:
The word 'Agni' denotes not only the intestinal fire, but also the highest Self in so far as qualified by the intestinal fire.--But how is this to be known?--'On account of impossibility;' i.e. because it is impossible that the mere intestinal fire should have the three worlds for its body.
Now, in the current sutra, Jaimini thinks that the word "Agni" can also be interpreted etymologically to directly refer to Brahman; as a name of Brahman:
Jaimini, on the other hand, is of opinion that there is no reasonable objection to the term 'Agni,' no less than the term: 'Vaishvanara,' being taken directly to denote the highest Self.
Jaimini is not saying that one should interpret all names and common nouns in the entire Vedas as referring directly to Brahman, but instead is saying that in the context of the Vaishvanara Adhikarana of the Brahma Sutras, that there is "no objection" in taking the etymological meaning of the word "Agni" to refer to Brahman.
What Ramanujacharya means is that, in the Upanishads, various common nouns and names of Devatas like "Prana", "Indra", etc. are described as having qualities that only the supreme Brahman can have; qualities like creation of the universe, being the Self of the universe, the self of all Jivatmas, the ability to grant moksha to everyone, etc. For example, in one place, "Prana" is said to have these qualities, and in another place, "Indra" is said to have these. There cannot be multiple Brahmans, so how do we reconcile these verses?
According to Sri Vaishnavism, the words either directly refer to Brahman through etymology, OR they refer to Brahman as the Antaryami of those things.
This is summed up nicely by Vedanta Desikan in the Nyaya Siddhanjana:
And in the portion concerning the cause etc. [of the world] [the Upanishads], it is proved that
words denoting various [entities] finally import the Supreme Self alone. Because their final import is One who has these [entities] as the body. Or because, like the words "akasha", "prana" etc., these [words can be interpreted as directly referring to the Supreme
Self] by means of secondary etymology.
When the individual selves, are mentioned in
teachings of the [Upanishads], [we first should try to understand] by
means of etymology and others that such a description directly refer to the
Supreme. If some of their characteristics cannot be established otherwise, its object is [the Supreme] as qualified by these [characteristics].
This interpretation strategy is a last resort and is only used in places where such interpretation is needed, like in the Upanishads.
There is no need to interpret "Indra killing Vrtra" as "Brahman destroying ignorance". Although it may have that as an inner-meaning, it's not its primary meaning.
