I rarely go over 10GB, if I have larger downloads I do them after midnight. For my usage PN is a superb choice, but for someone that downloads a lot using P2P, Usenet or download sites and expects near line speed Plusnet is not appropriate. That's why blanket "wouldn't touch Plusnet with a bargepole" type posts are totally inappropriate without knowing the sort of usage pattern required.
As you say, the usage pattern is vitally important.
However on the previous packages I could recommend the lowest one for someone's elderly parents being introduced to broadband, (and still these turn up remarkably frequently), as the equivalent Newnet was a 12-month contract and more expensive - the better Newnet throughput being irrelevant. I cannot really do that now with an 18-month contract in place.
Pro I still can recommend for low usage gamers, and the previous (non-Pro) 15GB package made a lot of sense in particular to Newnet Lite (3GB) users having to upgrade to the Newnet 12GB one at a higher cost than Plusnet 15GB. Several did this, but even then they were worried about the shaping. They were able to make the jump for the same reason I was able to jump to O2 - the getout clause.
I think the only acceptable package on Plusnet for now is Pro, but it is absolutely certain the sites like uSwitch will continue to bring in many poor mis-guided souls.
The marketing men are not wrong on the changes unfortunately.