The IIe is a II+ with the most desirable II+ upgrades built in.
The II+ is a II with Applesoft II BASIC and floppy autoboot in ROM, which can be added to the II.
The only things the IIe really supports that the original II can't, is double hi-res graphics, double lo-res, and the 128K upgrade option.
You can even drop in a different character generator ROM for the added IIe characters.
There are RAM upgrades beyond 64K for the II, but they are mapped differently than the IIe upgrade.
The IIe mostly reduced the chip count by integrating the circuit on to custom chips and it switched the type of RAM chips used.
The IIe actually has some slower buss interface signals than the II or II+ and some older cards can't be used in it..
The 65816 has some 16 bit register support, but no more than other 8 bit processors.
The Z80. 6803, 6809, etc... all have 16 bit support.
I'd actually say the 65816 is inferior to most of those because you have to manually switch modes to go back and forth between 8 and 16 bit, where the other CPUs have separate 8 and 16 bit instructions.
The 65816 even has an 8 bit data buss.
The 6502 is really the only "8 bit" cpu with only 8 bit internal registers.and the 65816 isn't any faster running existing code at the same MHz than the 6502.
The only significant thing the 65816 adds over the other 8 bits is the 24 bit memory addressing, and even then you are mostly dealing with 64K pages.
You can do the same thing on the other 8 bits with an MMU.
The IIgs isn't even the fastest Apple II model Apple produced. The IIc+ was faster.
The IIgs is hardly comparable to the ST or Amiga with their flat memory models, 32 bit CPU model, the ability to switch between 8, 16, or 32 bits from one instruction to the next, more orthogonal instruction set, faster clock speed, and 16 registers..
It always was a laughable comparison.
The only thing that begs such a comparison is 4 bit per pixel graphics with palette registers, and that's far from unique among 8 bit machines.