The most "GM-like" experience I've encountered in a modern commercial product is the Kontakt factory library. It has almost complete General MIDI 1 coverage, plus a handful of random additions (a dozen electric pianos, samples recorded from some vintage synths, an SATB choir singing six different vowels, several drum kits...)

The quality is good, but it's not in the same league as specialised libraries. There are usually only two or three velocity layers (for example, the choir can only sing a subdued "aaa" or an intense "AAA"). The orchestral instruments only come with a few articulations, and the guitars and pop brass only provide one articulation each. None of the instruments have sampled legato.

Unfortunately, I think this is probably the quality ceiling for a sample library with good General MIDI coverage. If you were to add more velocity layers, articulations and legato transitions, the number of samples would start to grow exponentially, and the cost of the library would grow to match. I'm not sure there's any way around it.

I went through a phase where I was trying to put together a really comprehensive collection of samples, but in hindsight it was a fool's errand - you'll get diminishing returns fast, unless you're willing to spend huge amounts of money. Accurately emulating a live performer is a nice option to have, but it isn't actually a requirement for making good music. Huge amounts of excellent music has been made using synthesiser presets, or using instrument samples which would be considered "cheap" or "low-quality" nowadays. As long as you're willing to adapt your compositions to the instruments you have available, rather than stubbornly writing string melodies which could only be performed by a real-life violinist, you'll do well.