What you are getting is normal, the 2.4GHz radio on the R7000 is a little better than older models, but its real purpose is for 802.11ac connections. That is a very large area, not to mention the second floor, to cover with any 2.4GHz radio.
If you want good coverage over a space that large with two floors you will need to add a couple of routers configured as wireless access points -- you can use inexpensive TP-Link routers, but you need to make an Ethernet cable connection to each AP.
If it is just impossible to run a couple of Ethernet cables, you can use powerline adapters, but you need to use the newest 600Mbps models (like the Zyxel PLA5205kit) to get good speeds -- over 100Mbps. If you only want to connect phones, then an older Zyxel PLA4205 model would suffice. You would need three adapters to place 2 access points.