What they probably did when determining difficulty and ilvls was look at the average ilvl of every lv50 character and use that.
Also, you're comparing an optional EX trial to something that is considered mandatory content for story progression. It would be better if you compared Shiva HM's ilvl, which is i80, completely negating your entire argument. I think what you're not noticing is that HM trials, which all of these are comparable to, usually have a significantly lower ilvl requirement than EX trials, which there are none of in 2.5.