From convos with potential acquirers, common feedback has been that the holdco with multiple acquisitions is better positioned to be acquired later down the line with a much cleaner cap table where the subsidiaries are wholly owned by the parent company.

They've mentioned that the various owners of different acquisitions have different levels of equity rollover can get really messy in the full acquisition (even with drag-along clauses).

What do you think?

Many lawyers call "Phantom Equity" a "Profits Interest." Others call it a "Carry." All basically the same. It is a highly documented area. The key theme is that the equity is earned over an agreed upon investment return hurdle. No matter what you choose in the realm of Phantom Equity, Carry, Profits interest, Earn-out, Seller Note, IOU on a Paper Napkin, etc., you should expect to have continuing, detailed conversations with the seller after closing about the instrument's calculation and value.