408 hyd roller, too much spring pressure?

BH's DO require lighter components. The synergy is that their shape has an intrinsic weight loss from a smaller retainer.
The requirement stems from the fact that you're losing spring mass. Less mass means less energy the spring can absorb - there's no free lunch.
Not necessarily. Mass absorbs energy but it also releases it in the form of heat. The transfer of energy from one mass to another (ie: steel spring to air/oil) is a function of surface area.

Valve springs absorb kinetic energy (movement of mass) and store that energy until it is released. However – as you rightly pointed out that there is no such thing as a free lunch – some of that kinetic energy is converted into thermal energy, which is released by the spring mass when it comes into contact with oil and air (conductive and convective heat), and to a lesser extent the other metal surfaces it is in contact with (valve seat, valve stem/retainer etc).

A spring with a smaller mass but a larger surface area (an ovate shaped spring, for example) is able to absorb more energy because it is able to transfer excess energy at a faster rate. The more energy a spring can release in a given amount of time, the more total energy it can absorb in that same amount of time.

Distribution of mass determines rate of energy transfer.

Greater surface area = faster heat transfer = less stored energy.

In addition, lower spring rate = less pressure = less heat = less energy transfer to begin with (they are all the same thing).

Finally, what came first: the chicken or the egg?

A beehive or conical spring, by design, is always going to have a smaller retainer. Suggesting that a beehive needs a smaller retainer (less weight) to control the valve-train is an oxymoron: if the spring didn't have a smaller retainer in the first place, it would not be a beehive.