So I tried to make this case before, but I think I went about it the wrong way.
Temple Guard are woefully insufficient to fill all the endgame infantry needs of any faction. Why do I say this? Every other faction - literally every single one - has a high-tier infantry option that is basically an upgraded version of one of their beginner infantry units, and is effective in an infantry vs. infantry slugfest.
Empire have Greatswords.
Vampire Counts have Grave Guard.
Greenskins have Black Orcs.
Dwarves have Ironbreakers, Hammerers, and Slayers.
Chaos has Chosen.
Beastmen have Bestigors.
Wood Elves have Wildwood Rangers.
Even Bretonnia, a hugely cavalry-focused faction, has Foot Squires and Battle Pilgrims.
As far as game 2 races, High Elves have Swordmasters and White Lions.
Dark Elves have Executioners.
Skaven have Stormvermin with sword & shield, as well as Plague Monks.
Tomb Kings have Tomb Guard.
Even Vampire Coast, a mostly range-focused faction, have Depth Guard with dual axes.
Lizardmen are the ONLY faction in either game who do not. How does this make any sense, since they have some of the best early-game infantry?
Long story short, we need a Temple Guard with hand weapons option. It wasn't so bad earlier because you could rely more on your big dinosaurs, but ever since they removed the healing from Cold-Blooded, Carnosaurs have become walking arrow magnets.