The main differences between the two include:
Budget: Templates are inherently cheaper than customisation
Time: The same applies - templates are quicker to use and apply accordingly
Brand: Customised material tends to outperform templates here
Functionality: Akin to branding, so custom wins here even for SEO too
Flexibility and scalability: Custom based sites are more adaptive than templates
Nevertheless, templates are more reproducible than customised ones, as are the associated pathways with landing pages, for instance. Ultimately, templates are becoming more intuitive and smarter, courtesy of AI protocol plus machine learning.