Typically, the large antenna arrays are what give qro stations their big signals, not the qro.
Well sometimes you need both the amp and the antenna, but the point is a good antenna system will improve both
transmit and receive power. What I find amusing is how on the Internet at least, I've come across at least a couple people who seem to think the power amplifier on the receiving end makes one hear the QRP operator better. These must be the same people who buy an expensive inert decorative item to place on their stereo system which will magically improve their audio in proportion to how much they paid for it.
I plan to spend at least as much effort and expense on antenna construction as I paid for my FT-817. After passing that point, I'll get an amplifier kit as well. Nothing wrong with QRO, but use only as much power as necessary for the intended communication.
I routinely hear and work guys using 5W with an efficient antenna/feedline system who have very good signals.
I personally experiment with antennas all the time, and am currently building a rhombic pointed at Japan.
I think my 5W will be enough to get me heard, but time will tell.
Of course if I pumped a KW into the rhombic, I would have no problems at all, but for my personality there is no challenge in that.
That is the essential point many qrp critics fail to recognise, its not the capture thats important for some - it's the chase.
I also like to do bow hunting with a recurve, so my ham radio orientation leans in the same direction.
Others use rifles or compound bows - it's the persons attitude to hunting and their prey that defines their gear.
And in the end, its Effective Radiated Power (ERP) that's important.
Every QRP enthusiast knows (or should), that they should use the best antenna they can, within the limitations of their circumstances.
But of course, part of the fun of QRP is that you can put your gear in your backpack, and with some light batteries, and a solar panel,
trek into the wilderness and run for weeks.
QRP is more about a state of mind, and the freedom to do things you cannot when chained to a vehicle or house.
73 - Rob