The benefit of Ephemeron is you get 3% Haste which allows for a looser build for TPing as you are not limited so much on TP gear. The advantage becomes very useful when stacking alot of Attack, STR, and Double Attack, with the extra space provided. Such as if you are using Ephemeron you can cut out 3% Haste from your build, meaning Eurus' can be taken out, removing -STP and instead you can put in something like Dusk+1, or Ghadhab for the Attack. You can also use Kudzu more comfortably because though it does not give haste it still becomes more easily worked around. As it stands without Phos you are forced into a build of Phasmida/Ninurta's, Zelus, Brego/Alucin, Calmecac/Rubeus, Eurus', which puts you at 25% Haste. With Ephemeron's 3% Haste you are able to use a few more varied pieces with stats that surpass Shikargar's stats in the end, which just like Saeval said, "The stats on any particular slot doesn't matter, it's the total stats of the build that are important" and that is why Ephemeron is good, it helps the overall build rather than just being a good item on own.

STR Shikargar is good for the attack & STR, however if you can make this up with the gear you are able to use thanks to the 3% haste than it loses its effect for the most part and becomes much less useful. The benefit that Ephemeron can not mimic however is in WSs, as you would already be stacking stats as high as you can regardless of the AGI, DMG, TP Drain, or Haste that Ephemeron gives, thus for WSs STR Shikargar is massively better. In TPing however its effects can be mimiced by gear you would use thanks to the 3% Haste on Ephemeron that you would need not worry about any longer.

I would argue that if anything STR Shikargar might be better off with Excalibur and Ephemeron better with Almace simply for the fact that Shikargar with the STR & Attack play more to the benefit of Req & KoR thanks to mods & Req's attack penalty. However both weapons have their merit, and to think either one is the be all end all of offhands seems like a flawed perspective to me because you can not ignore the 3% Haste Ephemeron gives to a TP build, nor the STR/Attack Shikargar gives to a WS build.