Interesting thoughts, but I'm not sure I agree.
- There is transparency among bid bots thanks to @yabapmatt's steembottracker.com. Everyone can see how much they will get at least / at most and can choose the bot that has the best rules for them (ok, given that there aren't many last minute bidders). That also includes the fee (if any applies). 
- It's not only whales auctioning their votes, but any size or type of bots. 
- Auctions are an effective price building mechanism especially when liquidity is low. In addition, your example with Bitcoin seems odd because votes are typically auctioned in fractions. 
What will a "decentralized" bid buying system look like? How will it actually improve transparency and fairness? Could you provide details? I'd be happy to help :-)
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allow anyone to sell their vote for whatever price they choose without taking a cut. problem solved; free market achieved.