It is all about the accent of which country you are referring to. If you pronounce awesome as “ah-sum” and arson as “aa-son” (with little to no emphasise on the R) then there are similarities in phonetics But in Australia we pronounce it as “Oh-sum”. And there is no way to pronounce arson as “oh-son” or “ore-son”. Not in Australian at least.

As an Australian speaker, its not possible. "Awe-" rhymes with more, four and poor, whereas "ar-" has the same sound as car, spa and Panama. Our Olympic rowing team was called "the Oarsome Foursome", partly for the rhyme, plus our missing R makes "oar" and "awe" sound identical. Even with a US "R" and mispronouncing it as W, I couldn't confuse the two. The vowel sounds are simply different.

In many American accents, the AW in “awesome” and the A in “arson” are indeed pronounced the same, but those accents all pronounce the R in “arson”. Non-rhotic American accents (which may still be heard on the east coast) distinguish the two words in the same way as the British and Australians do. Additionally, all native English speakers would certainly distinguish between the N and the M.