Based on those requirements, especially the 1Gbps speed, Asus GT-AX11000 would be the closest to saturate that speed along with decent distance. The Asus AXE11000, AX6000, AX5400, AX86U/AX5700, and RT-AX89U would also be good dual-band candidates to be reliable, offer good VPN, and get as close to the 1Gb/s speed. For Netgear, I would say the RAX50/50S due to the removable antennas, or RAX70/80/120/RAXE500. With Netgear I would lean more towards the Nighthawk version that uses the DumaOS. TP-Link is also not bad and would stick with the Archer AX90/AX6000/AX11000 series.
For Merlin support, the Asus RT series of routers will typically get supported, but you would have to check. The Stock Asus firmware has gotten better and has a recovery mode should anything go horribly wrong firmware wise. Netgear can sometimes be quicker on firmware as they mainly just a networking company and have a big support base for that. Does not mean they always are quicker, but in a lot of cases they are.
I would say you don't want to skimp and go to cheap, as you may find out features/support may not be completely there and to actually achieve as close to the 1Gbps speed, you will be paying up front for the hardware. I also as you can probably see, I am stating to achieve close to the 1Gbps as real world, speed can and will be lower based on hardware, distance, interference, walls, etc. I have the ASUS GT-AX11000 Wireless Router, and on Wifi I get an avg speed between 300Mbps-600Mbps Down and 10Mbps-18Mbps with minor changes in settings to optimize that performance running speed test. It will also depend on the receiving hardware too, with the primary part of course being the wireless card. Other then speed, this would be my 2nd ASUS router, as reliability has been great and the AX11000 replaces and at the same time compliments my older RT-AC3100 Asus router running in AiMesh. Price and choosing of hardware will dictate what performance, features, and reliability you get.