But unless the cartel has 100% of has power, which is impossible, these transactions would simply wait for an honest miner's block.
This is incorrect. A cartel with a high percentage could,
within the protocol, reject blocks that don't follow its transaction inclusion rules. It doesn't take 100% to completely block some or all transactions from the chain.
A miner does not reject blocks, a miner can only build on top of a chain of blocks.
Yes, you have a chain of A -> B -> C
Normally the miner would build on C, but if a cartel with a high percentage wishes to reject C, they simply build on B instead.
What you are describing is an attacking miner only building on top of their blocks and not on top of any blocks. That is the very definition of a 51% miner attack. The reason an attacking miner needs 51% is so their chain, that only includes their blocks with their inclusion rules, grows faster than the rest of the network.
Somewhat. It doesn't have to be only their own blocks, it can be other blocks that follow
their rules.
I don't remember a proposal from Gavin to defeat this sort of 51% attack, just his IBLT proposal which gives an incentive to include the standard set of transactions, but only to a miner that isn't large enough to define this standard. Given the ability to "set the standard" IBLT might give the cartel more power, I'm not sure.