Model 3 maintenance is exactly cheap, either:
https://www.tesla.com/ownersmanual/model3/en_us/GUID-E95DAAD9-646E-4249-9930-B109ED7B1D91.html
- Brake Fluid Exchange and Cabin Filter every 2 years ($3-$400)
- Clean and Lubricate calipers annually ($200?)
- A/C Evac and Recharge with desiccant bag replacement every 6 years - 1234yf is extremely expensive. Evac/recharge alone is $5-600 at most places, plus the desiccant bag replacement. You're probably looking at $800-$1k.
So no, I don't think the Model 3 is significantly cheaper to maintain than your GTI if we are talking about scheduled maintenance.