how strong is strong in the posterior chain?

GHP,

Bringing up a weaker bodypart is just that....bringing it up. In the case of bringing up hams, you should still be doing lifts that work the quads as well. The idea is to do extra lifts for the lagging part, such as doing two extra ham exercises at the end of your workout. However, while doing this, you should still be continuing to strengthen the quads at the same time. This will not only help with increasing overall strength, it also lessens the chance of getting injured.

As far as foundational strength, you never really want to break away from building it up. There are advanced methods of training that can be used to get over the edge or bust a plateau, but for now at your training age, sticking with the bread and butter lifts is the best thing you can do.