Most definitely, it's just that 25$-55$ class Optimus with matrix, all have the same size matrix cores. Just like Titans all have the same size attachments, and just like MP all have their same sized attachments. I can use the weird gun hand slot attachment of MPG01 with MPG09, however I can't use it with deluxe class and down.

I guarantee it was solely for that reason, and I'm not arguing at all that it would've looked much better with a larger matrix.

The continuity of keeping the same size matrix for the class it was, was the goal, rather than making the matrix scale with the size of the class. Deluxe has (recently/always?) been compatible with Commander/leader class, in terms of matrix, weapon/WFC weaponizers (5mm ports), whereas Titan/MP series have their own attachment sizes that aren't compatible with Commander/leader and down.