Question tp link archer c7 -- increase range/strength

Although I would have to dig thought the FCC data base to be 100% sure I suspect your archer is transmitting at the legal maximum. Your problem could be the end device and not the router.

Almost all routers will have more or less the same range. There is a very small difference in some cases but it depends so much on your house it is completely unpredictable which if any device would work slightly better.

The best option is to run ethernet cable to a remote room and use a new source of a AP.. to provide wireless. You can use powerline instead of ethernet but it is not as fast.

After than you start looking at repeaters or mesh systems. These tend to not perform nearly as well as other solution but if you have no other way to get signals you can live with a poor solution is better than nothing.