True- considering how hard they leaned on Concentration as a mechanic for spells, I was flabbergasted that Spiritual weapon had just a regular duration.
Even more so when I read the fine print, that said you can move the weapon- and get a second attack as a bonus action.
One could also simply use Improved Invisibility from a prior edition- perhaps copied off an old scroll found in a dungeon, or in an old spellbook, left behind in a past era. (or found in an old Lich's lair!) I've been doing that a fair amount, considering I'm running adventures written for AD&D, converted to 5e. Star Cairns had that built in! Old magic research/ construction factories built by Suel wizards and abandoned 400 years ago. Many of the vaults were still sealed. It's a cool thing for adventurers to find oddly functioning magic from times they only know from legends!