This is true for MVP-like designs which require exit priorities.
Both attacks you describe here and in Chunked Plasma Exit Games with Expensive Griefing do not apply for Plasma Cash-like constructions with rootchain enforced non-fungibility.
In these constructions you are never forced to exit a coin because the cheating party (operator) is required to add a separate security bond for each exit of a coin (or slice). Each exit is separate from others and has its own dispute period. Assuming liveness for challenges and that the exit-game is incentive compatible, we can expect that the operator will not try to attack if they are to lose money.
(You can additionally burn part of the challenge bond, if you consider that the operator is also front-running challenges - context: Plasma Front Running problem)
As a result, each exit is individually challengeable which means it suffices to challenge exits involving coins that you own to maintain safety.
This also applies to Cashflow/Prime designs, given that if an operator attempts to exit a large slice of coins, a challenge involving any coin inside this slice is sufficient to cancel the exit.