Hi Peter,
I assume, your question is about subsystem/SoC environment, where the individual IP’s verif. environments are integrated to create a top level env. There are very high chances that the individual IP’s are sufficiently complex that virtual sqr, virtual seq API’s (that helps generate some working scenarios) are part of the delivered VIP itself.
In such cases you cannot avoid having multiple layers. In-fact this layering mechanism will be really useful for you to integrate things at ease.