Hi Max!
I agree with Orikad, at least three elements need to be changed/eliminated to prevent looking too much like a Roman Soldier. Here is a list of items that together stand out as making this a crossover:
1. Shoulder armor
2. Chest armor
3. Shield
4. Baltea (studded strips)
5. Spear
Choose any 3 to change/eliminate and it should be able to pass.
My recommendation to keep the aesthetic and stay Mando would be to change the shoulders to exactly match legacy references as seen here:

And more examples can be found in the reference library:
http://mandalorianmercs.org/forum/index.php?topic=153459.0This shows that Legacy shoulders are solid and the bicep part is all that is layered. This way, the entire upper body is un-mistakenly legacy Mando.
We know spears are Mando because of the Beskar spear references, so I think that is fine as it is too.
That means the other two elements to change/eliminate would be the shield and the baltea. The only shield Mandos use that is close to this, is the Mandalorian Guard.

If you change the shape of the shield to match this shield reference, you'll be fine because it's more "in-universe."
At this point, with all of the other elements solidly based on Mandalorian references, the Baltea should be ok to stay, but I'd still recommend altering them to make them slightly different from the Roman style, maybe thicker or thinner straps, for example.
I hope that was helpful! I'm looking forward to following your new build. I love your drawing as well, it is very cool!
Sincerely,
J'Khara