Liquidity and Spread Risks from Brokers Used by Prop Firms

I've been trading with several Prop Firms for a while now, and I've noticed something I'd like to discuss on the board: the liquidity and spreads offered by each Prop Firm's broker. Sometimes I see huge differences in $EURUSD spreads, or during major news events, $XAUUSD spreads can widen alarmingly. Plus, there are often unusually frequent requotes or slippages. These issues directly impact our risk management and position sizing.

The point is, as traders using Prop Firm capital, we don't choose the broker ourselves, but we have to bear the consequences of the infrastructure they select. If we encounter a broker with poor liquidity, wide spreads, or frequent execution problems, it's like having one leg tied. I'm curious if anyone else has experienced similar issues, and what methods we can use to assess these factors more deeply before deciding to trade with a Prop Firm, beyond just looking at a rough spread table or asking basic support questions?