Possibly, at least compared to the previous M4 generation. For the lowest tier M models to this point:

  M1 (any):  4P + 4E
  M2 (any):  4P + 4E
  M3 (any):  4P + 4E
  M4 (iPad): 3P + 6E
  M4 (Mac):  4P + 6E
  M5 (iPad): 3P + 6E (claimed)
  M5 (Mac):  Unknown

It's worth noting there are often higher tier models that still don't earn the "Pro" moniker. E.g. there is a 4P + 8E variant of the iMac which is still marketed as just having a normal M4.

Are these cores getting way more complex? Because there should be room for 2x - 3x as many cores with die shrinks at this point.

The die shrinks are less than the marketing numbers would make you believe, but the cores are getting significantly more complex. I think E cores had a 50% cache increase this generation, as an example.

The above summary also excludes the GPU, which seems to have gotten the most attention this generation (~+30%, even more in AI workloads).

If you get more space, you need a really good reason not to use that space on more cache.

Also, the size numbers are lies and aren't the actual size of anything.