1. Tamil Brahmins have a 'presence' in Trivandrum, not a 'significant presence'. They constitute less than 0.5% of the population of Trivandrum.
....there goes your credibility.
2. Kingdome of Travancore (south tip of kerala) employed some Tamil Iyers, some but a LOT of Namboothiris who are Kerala Brahmins. Only a handful of them became diwans of the King, this position was later usurped by the Thampi's (who are Nairs).
3. Most Tamil Brahmins in Kerala belonged to the Vadama and Brahacharanam sub-sects. Iyers were usually employed as cooks, musicians and temple assistants, since they were not allowed to conduct pooja as the priest (shanthi) in Kerala temples followed Tantric rituals.
4. In fact Kerala Iyers and other Tamil Brahmins were ranked below the orthodox Nambudiri Brahmins in the caste hierarchy and the touch of a Tamil/Kerala Iyer meant that the Nambudiri was defiled by Eda Shudam which required the Nambudiri to bathe before resuming rituals.
4. As you can now conclude, their influence was minimal except maintain the general guidelines of Hinduism which remains common all over India and for all Hindus.
5. Iyers who settled in the north of Kerala i.e. Palakad did much better.
6. Malayalam is a mix of sanskrti and parts of tamil. 'Mallus' have no reason to be offended by facts, the same way tamils have no reason to be offended by facts.