There's consistent Y columns, but the wider opening over the staircase required diverting the load that would have travelling down the Y to the adjacent columns.
I think it would have looked better if the grand staircase was centred between Y columns,
then there'd still be symmetry, even with the extra crossbeams.
Here's the load distrubtion I see.
Similar to this structure at the Hootsuite Building on 4th for the garage entrance.
But in that case, it's one column distributed to 2 columns. You can see that the beams are also thicker too.
In the above case, it's 2 columns concentrating to one then distributing back to 2.
Pic by City of Rain, SRC.
https://skyrisecities.com/forum/thre...259418&slide=0