Something does not add up. You are a high net worth client and this is a large transaction. We are not talking about 100K condo. So typically both parties should have excellent representation. Why did your agent not advise you to write the offer? They are well aware of the fact that the agent has to at least present the offer to the seller.
I tend to believe that the sellers are more of the challenge than the agent. The seller is letting the agent know up front that any offer other than full offer is unacceptable and will result in them finding an agent who can better represent them for full asking price.
The agent should be firm with his client to garner some flexibility but they were probably leveraged by the seller when they iniitially took the listing. They might simply be relating the opinions of the seller rather then recognizing that their job in this instance might be to sell their own client on the offer. JMTC