Prop Firm Payout Reliability and Underlying Broker Liquidity - A Growing Concern

Been trading with a few prop firms over the last year, and something that's really started to stand out is the variability in payout experiences. It's not just the speed, but sometimes the actual ability to move funds, especially after a particularly good run. It makes me wonder about the deeper infrastructure, specifically the brokers these prop firms are using in the background.

We hear a lot about spreads and commissions, which are obviously critical. But if the prop firm's underlying broker isn't solid, or perhaps more pertinently, isn't offering the prop firm itself sufficient liquidity for our profitable trades, does that translate into payout friction? I'm not talking about scam firms; I'm talking about the ones that seem legitimate but occasionally run into 'technical issues' or 'bank transfer delays' that seem disproportionately affect larger withdrawal requests. Are we, as traders, essentially tied to the liquidity health of the prop firm's prime broker, and how much due diligence can we actually do on that front before committing to a challenge? What's everyone else's experience on this, especially those dealing with larger capital allocations from these firms?