It's a computer. A computer can only do as good a job as the information you put in (garbage in - garbage out). If it doesn't work out as expected, don't be too quick to blame the computer.
Complete the descent forecast page with the most accurate information available to you. TAI ON/Off is often overlooked and can have a big influence on the descent profile. ISA deviation is a tricky one, since Boeing says it should be the 'average ISA deviation during the descent'. Ideally you should have winds in there down to platform altitude. If you lowest forecast wind is at FL180 it will assume a linear reduction to zero between FL180 and ground level. Don't put the cruise wind in the descent forecast page. It's a waste of one of the entry options in the descent forecast page, and is better done in the route data on the legs pages or on the 'perf init' page by putting the top of descent cruise wind in there.
After you have done all that, monitor the descent and be ready to intervene if required. Actual winds different from the forecast winds (does happen), ATC speed constraints and/or short cuts can throw your VNAV path descent out. I think the biggest issue with using VNAV PATH descent is knowing when to abandon it.
One can reduce incidents of DRAG REQUIRED messages with fake tailwinds, but then the speed can also become irritatingly slow too.
A fake tailwind causes the A/C to descend too early and increases overall fuel burn. VNAV PATH is not a speed mode, so by definition the speed cannot be low. VNAV PATH works with a 'target speed'. If the speed gets sufficiently below this target speed, it will correct by increasing the thrust (or give a 'thrust required' scratch pad message). Don't put deliberate garbage in the computer, the result will be garbage from the computer.