Look at the weapons mix in a WW II infantry squad (not just what TO&E calls for), but what was common in the field by the end of the war.
It was a generally a mixture of Garand, M1 Carbine, Tommygun, and BAR. And pistols. No one gun was expected to do it all well, nor was one soldier expected to do it all well by himself. The different arms supported each other, each one "taking point" when its strong suit was needed.
Today, we incorporate the carbine, and SMG into the assault rifle. Nearly everyone has what amounts to a LMG carbine. And still, dedicated long range rifles are needed, as well as GPMG support.
Keeping in mind the design limitations of the era, I think the M14 was an excellent rifle. It is not an excellent carbine, it is a miserable submachine gun, and its a poor LMG. But it's a good rifle.
Are there better rifles? Opinions vary, but I think a case can be made that there are better rifles for many applications than the M14. But there are also many which are worse, for those same uses.
Bullpups? They get the nod on overall length, and still having a decent barrel length, but bullpups have their own issues, and so far, no design has gotten past all of them.
They balance differently. They are not ambidexterous (and while some can be switched, it's an either, or, proposition. The long distance between the trigger and the action creates its own set of issues. Some designs manage this well enough, others...lets just say that it is a difficult thing to get, and keep a good trigger pull in a bullpup automatic. It can be done, but I don't see it being done for general issue rack grade guns.
Rifles in "standard" configurations are at least marginally usable by both right and left handed shooters without any modifications. Until someone comes up with a design that ejects out the bottom, bullpup autos must be either right or left "handed". (this issue also comes into play firing around barricades, although not just with the bullpup)