Well that model of Hytera is only 3watt and has a very small antenna. Probably not even transmitting 3w with battery age/use. In any event they will be outclassed by a 5watt radio with a bigger antenna like what the UV-9G has. So, the test result you've seen has plausibility. The real question is what type of building & topographical interference is in the area that is causing the need for larger radios?
GMRS is a licensed service. So, as long as everyone gets a license, you have some GMRS radio options out there, but really a full keypad radio is not a good option in your setting and end users.
Thus, here are some business radios that make sense for you.
Look at the Hytera TC-508 (dual band), PD402i-U1 or BD502i-U1 which are much better alternatives for your environment. Also look at Motorola CP100D, Motorola RM RMU2080, Icom F4001, Kenwood NX-P1302AU.