At 15 it is an high impedance 1/2 wave antenna so the matching network does fine.
Coax used better as LMR 400 SWR on 15 1:1.3.
Working every continent there so if it was a leaky dummy load there explain please why it works as good or better as my Fritzel FD-4 at 40 feet up also fed with better as LMR 400 Coax.
The only difference i see is polarisation differences, sometimes the FD-4 wins sometime the Imax 2 K wins.
Even on 18 MHz it works decent though there it needs the tuner for the swr is 1: 2.3.
Same as 15 meter the FD-4 wins sometimes, sometimes the Imax 2 K wins.
If i would have large losses using 1000 watts into it which i did over longer qso's it would have burned out the matching system on any of the bands used.
losses of an trap are about 0.5 dB add several traps if you work with a multiband vertical trap antenna.
Don't forget trap losses add up in multiband verticals...
and mostly have a much narrower bandwidth.
Traps also form a weak point in the antenna and need decent weatherproofing all the Imax 2 K does not need bar the antenna plug.
So for 10/11 and 12 meter i have an full 5/8 antenna on 15 and 18 an 1/2 wave antenna.
Every trap antenna uses 1/4 wave sections for the bands, traps with losses to couple the next section for the lower band etc.
Even on 18 where the swr is a bit off with low loss coax i have relative low losses with a good tuner.
on 15 where the system is good almost no losses.
As on 12/11/10.
I don't work 11 bar the 1 x a year saying hello to a good friend there.
So, with all due respect i don't go with your observation.