I am going to go out on a limb here and say that many years ago when consulting for an auto business one task was looking at future engine specs for their FWD platforms. The I6, V6, and I5 were considered. My memory isn't all it could be given the timeframe, however the I5 delivers a harmonic of one higher magnitude than the I6. This combined with the even firing interval for the crank config made the engine very smooth. It also provided a good balance of bore spacing vs engine width (trans space being critical)

The end choice was an I6 purely because the marketing viewpoint won and trans engineers said they could do a compact box). The 90deg V6 was a nightmare except if offered manufacturing modularity for future expansion into larger engines.

For an ultimate affirmation of the I6 however, look at truck engines. These have worst case scenario for vibes etc due to reciprocating masses (some are now at 17litres and 650hp) and are almost exclusively I6s. Higher end are now returning back to V8s.

Now, if only I could find my calcs for the I5???