Thanks again, Christian.
I can appreciate the hedging given the complexity of ES and variety of configurations out there.
I think what we're saying here is, for indexing performance, all things equal, document size matters more than field count, probably by a large margin.
Just how much margin is a question. The best way to know for your particular situation is to benchmark, varying the factors you're comparing.
I might start by testing one hundred tokens in one field versus one hundred tokens spread across 100 fields.