I suppose you are using the Premium version?
In my opinion your analytics team will find it very hard to show the ROI on using Premium compared to Snowplow. After all the main reason Google is charging a fortune is because of the data.
in other words, in order to collect all of your data, store all of your data, get analysis that is based on all data and not sampling, etc. Google is charging big money. Why do that when you have a much more powerful tool that cost a fraction of that?
if all your analytics team is using is the standard reports in Google then you might say that the premium is also for the ready made reports. But if that is the case your team stil has very basic capabilities.
If you have more advanced capabilities like data science team then you want access to data. I assume that when you say "big query" you mean pushing the data from Analytics to big query and not simply using big query as your storage for the snowplow data, because that is doable.
So what is the point here? what is the added value that you get from using Google and how much is that worth that you are willing to pay so much money for the same data (and much more) that you can collect with Snowplow at a fraction of the cost?
i'm still waiting for someone who can explain to me how they justify this cost.
Lastly and most important for me is that the Google analytics approach is a dead end. all you can end up with is an analytical use of the data with very high costs. once you start using real time pipelines a whole world of possibilities opens up for you. in our case we are using SP as the basis for real time product and marketing capabilities - recommendations, classifications, anomaly detection, running a rules engine and more. no chance to do that with Google Analytics.
Google and Adobe have great sales team who are experts at doing cross sales and up sales to their clients. it doesn't mean that you need to fall into this trap.
you are paying a lot of money for an inferior technology with limited scope, full dependency on Google and get very questionable ROI for that investment. I will push the analytics team to make a real comparison and focus on the money