I thought the idea to go mirrorless was to have something lightweight and easy to carry.
This is a recurring misunderstanding of why people choose EVF cameras. Yes, the bodies are typically smaller and lighter, so the overall kit
can be less bulky
if and when that is a priority, but bulk is far from the only motivation for preferring an EVF camera over an OVF one, and it does not rule out there being other times when a fast and therefore bulky lens is needed.
For other reasons besides bulk as to why some people prefer EVF cameras, see any of the many discussions in these forums! (For me, #1 is magnification during manual focusing, #2 is the option to "gain up" the EVF image in low light situations, and in smaller formats like Four Thirds, another is the larger/brighter VF image size possible.)