Dynaudio C1 compared to Harbeth Super HL5 plus?

It is silly to compare any Harbeth to an Electrostatic speaker. Electrostats are fast and transparent speakers. They dont have any extra bass bloom in general. Harbeth is totally opposite. They are warm and bloomy speakers. They are not really fast or transparent like a ESL at all. An ATC is much more like a Electrostat in that sense. Harbeth is good in other ways. It is warm, forgiving, easy to listen to.

Are Harbeths deficient in bass and high frequency extension?

Nope. 

I've owned them both

the harbeths are much easier to drive than the dynaudios. The harbeths are smoother and have almost no listener fatigue at any volume

the dynaudios need a ton of current and are voiced to play loud t sound their both, yet the dynaudio is a fabulous speaker in its own right

i prefer the harbeth

i now own harbeth 40.1s
they kill anything I have ever owned including Avalon eidolons

Both great speakers. I haven't heard the C1 in quite some time. I enjoyed them but recall they sounded best when played a bit louder than I like. I'm about to order the SHL5 Plus in Tiger Ebony as a Thanksgiving present to myself. With the right amplification, Harbeth's can be played at very low volume levels and you don't lose anything.