That's not the full story. First and foremost, the drop rate is irrelevant if your goal is simply to nab easy Sacred Crystals and move on with your life. Second, a 10% drop rate is indeed low, but to make a fair comparison with other maps one must remember that the entrance fees for low end maps are typically in the 20-50 Charisma and 1-3 Stamina range. Some of them are shitty and some of them are like Forest Front Line or Three-Sided Battle and offer decent extras alongside a cheap 10% shot at Silver units. It's a mixed bag but there's some value to be had if you pick your spots and do a bit of homework, especially on weekends. I'm sympathetic to the idea that newbies may make some poor decisions or fail to do research, but ultimately having more breaks doesn't really do much to address that problem.
Of the units you mentioned, I have exactly two and they live on my bench. You know what the big penalty for relying mostly on silvers, golds and Trading Post units has been for me so far? When I get to the tough-as-nails maps I sometimes settle for 1 and 2 star clears instead of 3 star clears. Missing out on that extra Sacred Crystal is mildly distressing but ultimately I'm still coming out ahead I've still been able to farm event units effectively via intelligent leaking.