This is not necessarily true.
In my case I bought an M0CVO LW-20 antenna for holiday use. This is a 20 metre long wire with a 9:1 unun. I tried it out in my garden. Now due to the very high noise level in my urban location when I installed it close to the house, I re-installed it with the unun halfway down the garden, about 25 metres from the house, which meant using a long run of coax to my tuner. This is why I said that the comment was not necessarily true, a long run of coax enabled me to use the inverse square law to reduce the electronic smog that I have to live with!
Actually the antenna worked surprisingly well, giving results quite comparable with my usual antenna, a 102-foot doublet that started life as a commercial G5RV - well it is still a G5RV as its originator preferred to use it as a doublet himself! After a trial over several weeks I removed it and re-installed the G5RV, the LW-20 is now packed away for holiday use.
Feedline loss was indubitably present with such a long run of coax, and of course it would be less with the 25ft of RG174 of the EARCHI antenna. I note that the data sheet for RG174 gives a loss of 8.9dB per 100ft at 100 MHz, with an operating voltage of 1500 volts. On the HF bands I would expect the losses to be significantly less than 8.9dB/100ft. It seems to me that 25ft of coax seems an oddly specific length, I guess that this length is integral to the operation of the EARCHI antenna.