Well, moving on from the use of tritanium and duranium as hull materials ought to do the trick. The former might in fact have been something introduced at the lower limit of the DSC-specified time window, because although it's found everywhere, even the ability to melt it (or to pour it into the shape that we then see melted?) is beyond TNG technology...
Timo Saloniemi
Well, there ARE materials today which can be burned and destroyed... but not melted in real life. Crosslinked polymers, both rubbery and glassy are such examples.
So, we can SHAPE things into those materials, and we can even recycle those materials (if we bothered to do so), but melting them is not doable (yet).
But on the other hand, the Federation CAN vaporize Tritanium (as evidenced from multiple examples - like the Borg cube)... just not melt it.
It seems strange that you can make/shape, vaporize and recycle a material, but not melt it (especially because usually, vaporization requires MORE energy compared to melting).
In "People of Earth" we learnt that the configuration and metallurgy of starfleet ships apparently changed around or after the end of the 25th century.
The changes seem to be big, considering that people in the 32nd century apparently had an easy time to recognize the approximate dating of when the Discovery was constructed after only being aboard for a short time.
So, let's discuss the possible changes.
Well, the Federation did have access to a disabled Planet Killer since the mid 23rd century, which was made out of solid Neutronium.
You'd think that Neutronium would be something the Federation would have been able to make on its own after about 10 to 50 years of studying that thing so that ships would have this alloy integrated into their superstructure by the 24th century, because 150 alien worlds working together with exponential developments and returns would EASILY make this happen with or without that 'trinket'... but, alas, we saw that starships continued to be made with a combination Tritanium and Duranium alloys in the late 24th century.
The 32nd century SF ships on the other hand DO have neutronium alloys (erm, FIBERS), along with organic, holographic ones, etc. (which actually seems more realistic for early 25th century Starfleet development).
If we take into account what was stated on-screen, we would probably have to say that SF managed to reproduce Neutronium by 25th century in great enough amounts for incorporating it into its ships hulls.
Its also possible that ships made out of 'solid neutronium' aren't particularly efficient. As we know from real life, mixing various alloys together to get the benefits of all those alloys with minimal or none of their drawbacks produces better results than just using a single alloy.
So, Neutronium (for example) could have become one of many base alloys used in starship construction past 25th century (and for all we know, Tritanium and Duranium could still be in use, just as supplemental alloys to provide their benefits).