I'm not sure that it was a question of hedging any bets, Magnum is all about getting higher-alpha cones, which means more alpha per hectare. If anything Hercules is a backward step for resistance - it's rather more susceptible to downy mildew - but it is capable of insane yields.
Because that's the market wants, consistency from year to year.....
And yet you yourself are using Magnum, when that could be substituted with a British bittering variety like Admiral or Pilgrim, which would also reduce food miles and (certainly in the case of Pilgrim) reduce pesticide usage.
With both malt and hops, there are elements of "commodity" and "specialist", where the former are essentially interchangeable and the latter where end-users are wanting a particular flavour and won't substitute with something else. Up until the late 20th century hops were primarily viewed as a source of alpha acids, and were generally bought on the basis of % alpha - obviously that's changed now and we're a lot more interested in their flavour contribution in late/dry-hop additions.
It's a bit the same with barley but the other way round - there are a handful of heritage varieties that are grown for flavour, such as Otter, Golden Promise, Chevalier and Hana but they are not much more than a rounding error in the scheme of things, well over 90% of barley is just a commodity for supplying sugar. As such, it's much more about the agricultural side as long as it's meeting certain requirements for malting. The way that happens is that each year a Recommended List is published of around 10-12 varieties that give the best yield, disease resistance etc based on extensive trials around the UK whilst meeting minimum standards for malting for brewing and/or distilling. Farmers can then safely choose one of those varieties knowing that they're best of breed and that they should be able to sell them into the market.
A big difference between hops and barley is that hops are perennial and barley is annual, so barley breeding happens much quicker (and as a much £££-bigger crop it has a lot more money put into it). Typically a variety lasts <10 years on the Recommended List, classics like Optic and Pearl were very unusual in lasting as long as 20 years. Being annual also means farmers are choosing new seed every year, allowing them to respond to changes in disease pressure etc much more quickly. So barley varieties come and go much more quickly than hops - this chart gives you an idea :
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