Of the three algortihms (Vintage Delay, Mod Delay, Tape Echo) that have pitch fluctuation as you adjust the delay time, I’d say that Vintage Delay has the least ‘time smoothing’ as you adjust the time. But it is still very noticeable when you try to control it with a square wave.
It’s not an ideal solution but you could try using the Looper as a delay by adjusting the DECAY value and leaving the looper in dub mode so that it’s always recording. Set the resolution to SMOOTH and use the PLAYSPEED to adjust your delay time. You should be able to adjust the speed here without any smoothing. It’s a bit clumsy and limited but it might be worth a try. You’ll hear a bit of aliasing at lower speeds so you might want to turn the FILTER parameter up a bit to cut out some of the high end.