I agree on the part of the opportunity cost and that given the transistor budgets of the time a simpler design would have served better.

I fundamentally disagree on putting the majority of the blame on the object memory model. The problem was that they were compounding the added complexity of the object model with a slew of other unnecessary complexities. They somehow did find the budget to put the first full IEEE floating point unit on the execution unit, implemented a massive[1] decoder and microcode for the bit-aligned 200+ instruction set and interprocess communication. The expensive lookups per instructions had everything to do with cutting caches and programmable registers, not any kind of overwhelming complexity to the address translation.

I strongly recommend checking the "Performance effects of architectural complexity in the Intel 432" paper by Colwell that I linked in the parent.

[1] die shots: https://oldbytes.space/@kenshirriff/110231910098167742

I huge factor in iAPX432 utter lack of success, were technological restrictions, like pin-count limits, laid down by Intel Top Brass, which forced stupid and silly limitations on the implementation.

That's not to say that iAPX432 would have succeeded under better management, but only to say that you cannot point to some random part of the design and say "That obviously does not work"