It doesn't literally do that. Given the numbers, if you assume (probably incorrectly) that a Tron/Steemit bloc would have no other support, then it probably couldn't vote in 17 witnesses, and certainly would have a harder time doing so. But with even some additional support (which IMO is likely given marketing/campaigning/etc.), they could probably still do it. Pretty damn hard to come up with voting rules that block stake that is 50% larger than entire rest of the voting population. This isn't just trying to block a tiny majority (say 51%), it is trying to block a very significant supermajority.

In doing so you inevitably weaken the chain against smaller-stake attackers. Still, the compromise may be worth it.

I doubt it is that complicated, and it could be possibly be done.