Short answer no.

Long answer: Mimo designs benefit from different array configurations with known and well placed antenna spacing. So once you hit "good enough" there isn't much of a benefit... But the loosy Goosy any direction antennas above the Xtreme routers... No, not at all

Best guess: each antenna is optimized for a different carrier frequency and splitting traffic between antennae allows the designer to use multiple, lower-cost parts on each data stream rather than a single, higher-cost part that can handle one antenna dealing with all the traffic.

Multiple antennae carrying the same frequency can make a difference, but consumer electronics where the end user has control over the angle of the Antennas likely isn't precise enough to make use of the potential benefits.

If the antennae were very precisely positioned and had very precise phase offset, the full array could be used to have very tight control over polarization...which really doesn't matter in a home wifi environment.

OR! It's just for looks.

Depends if they can be mapped to different channels/frequencies, then it’s possible you get more throughput assuming there isn’t some bottleneck elsewhere. afaik more antennae for the same connection, at essentially the same location, doesn’t make a difference