High altitude teas are not necessarily bitter, a DC by its variety is
high on the astringency leaning towards bitterness - most of the DC
and its variants I encountered in Hongkong in the past were dark
roasted to take off its astringency, but its bitterness lingers.

One way to counter this problem is to lower the temperature of the
water. For an easy approach, sufficiently cover the leaves with room
temperature water first, then fill up with hot water that has been
cooled slightly. Always take short brewing time for DC, unless you
want to do it the Chaozhou style, with full impact of astringency and
bitterness which might leave you light headed...

The other method requires some skills...easier if you use a gaiwan.
Bring the kettle spout as close as possible to the edge of the gaiwan,
and pour on the edge of the gaiwan. The leaves should float up gently
with the water filling the vessel. If the leaves start to swirl, you
would have failed. As much as possible do not disturb the leaves while
the water flow into the vessel. With this method you can let the tea
sit in there for a longer period and brew up a DC that is thick in
flavour without much of the astringency and bitterness.

Play with the DC, you'll get it at a perfect brew one day.

Kelmo