Incorrect. It is actually Rāma, Shiva, Krushna, Mahābhārata.

The suffix “a” is not to indicate “आ ki Matra” but to highlight the need to pronounce the suffix अ that is required in Sanskrit but we mispronounce in Hindi.

ā = आ
a = अ

हर व्यंजन में ‘अ’ जुड़ा होता है। जब अ नहीं जुड़ा होता तो वह हलन्त से दर्शाते हैं। हलन्त वाला व्यन्जन जिसे आधा व्यन्जन भी बोला जाता है, जब दूसरे पूर्ण व्यन्जन के निकट लिखा होता है तो वह उसमें मिल जाता है।

जैसे: क् + ल = क्ल (हिन्दी कीबोर्ड में भी यही पद्धति उपयोग की जाती है)

Having said that, many people do pronounce both the ‘a’ in Rāma in the same way and that indeed is incorrect. The first ā should prolonged, the second a should be short and abrupt.

For those interested in reading about the implied अ in all vyanjans, its available in all Hindi grammar books, which unfortunately both we and our teachers ignore and even on Wikipedia:

By the way, another mispronounciation of Hindi speakers is the devanagari letter ज्ञ

We think ज्ञ = ग्+य when actually ज्ञ = ज + ञ