I don't know what you mean by "competing for BTC units" since the chains don't really "get" the BTC units, more like just babysit them (unless the SC breaks).
i view the 2wp as a "pass thru" from which scBTC arise on the other side. these can then ride the SC themselves or be converted to InflataCoin or whatever. in that sense, scBTC cannot be harvested for tx fees on MC.
As far as competing for investment fiat, aside from just the tx fees which are negligible right now, this seems to also apply to Counterparty. A stock, for example, by nature involves investing in a company rather than in bitcoins (or dollars). Someone could buy ASICMiner shares for fiat or buy paper DOW stock certificates for yuan, but I don't know if that's a bad thing for Bitcoin or the dollar, respectively. Sure the money doesn't go into the ledger, but eventually just having a stock market running on the ledger, at bottom, should bring a lot of value to that ledger.
maybe.
i just don't see it. the other 6 billion just want stable money with SOV. i know i do. the deflationary nature of BTC itself means once fiat starts moving into Bitcoin it should send us to the moon. that is the asymmetric bet most ppl are focused on when they say that. it is a money thing. i simply find all these other things incredibly distracting and risky. and SC's violate "my" definition of the inextricable link.
These "pass thru" are a figment of your imagination. They are not unique to the 2wp and certainly not to a SPVP sidechain. They exist already in multiple form with the same consequence of risks to the ledger.