Yes, this is why my previous company never went the IPSP route (letting customers accept payments with your merchant account). They are incredibly arduous to get approved, you practically need to have a bank CEO as your godfather to get it. Also you need to be at least PCI Level 1, which involves actual auditors going through your business and policies. That part is significantly easier than the IPSP though. OP doesn't sound like they were trying to do that though. They talk about their client's individual Stripe accounts being turned off.
This is probably what a business like OP's would need to do. When their customers are small, use a processor like Paypal or Stripe. But as customers get larger, OP should probably do what we did: partner with an ISO, who can get the customer their own merchant account. OP still does the processing for them, but the risk and finances run directly through the client, not OP. The ISO can also add in a margin on the transaction fees for OP if that's part of their business model.
This is probably what a business like OP's would need to do. When their customers are small, use a processor like Paypal or Stripe. But as customers get larger, OP should probably do what we did: partner with an ISO, who can get the customer their own merchant account. OP still does the processing for them, but the risk and finances run directly through the client, not OP. The ISO can also add in a margin on the transaction fees for OP if that's part of their business model.