I have not tested the "Delrasha" (6p tal 4p del) build at all but from what i've heard, the slow time dot is your main damage source where it's amplified to i think 12k% dot instead of 2k% (not sure about the numbers atm) so a crown of primus for this build sounds promising - That's also what the delrasha wizards i saw were running.
I'd say just test it out. Run with both setups for a while and see what feels better for you. I think since the main damage source is the slow time dot, then having the utilities and buffs from all slow time runes is worth it. If meteors were your main damage source then getting max meteor damage would have been your number one priority.