The point of the seasonal artifact is twofold one it matches the theme of the season. This season is the Season of the Undying which is themed around the Vex. Now what damage do Vex mostly use? Void. And what shields do Vex have? Arc and void. The other reason is the artifact is meant to test out some unique ideas and builds. And this season is testing out unique mods for arc and void. It's not forcing us to use the subclasses they want us to use. It's giving us some unique options to test out with certain subclasses. The next season is the Season of the Dawn where solar mods will be the focus of the artifact and maybe some other interesting and unique mods. To have the artifact have mods for every element and subclass not only does it defeat the purpose of the seasonal artifact it also hurts it. To just match all elements and subclasses goes against the purpose of the artifact being season themed. How does solar fit with the Vex? That's Cabal themed very few Vex do solar damage and they don't have solar shields. And it hurts the artifact because it means less mods for other things, they have to remove certain mod ideas to allow there to be room for all 3 elements. For a long time now solar has been the go to subclasses to use. Well of Radiance was a necessity in too many activities, Golden Gun was the absolute god for burst damage, Blade Barrage was devastating for single target and mob clear, and Titans had melting point. Solar subclasses came out above arc and void subclasses. Now with the updates and the seasonal artifacts Bungie wanted to make the other classes more viable and give a reason to use them. When Season of the Dawn releases we'll get mods for solar classes to make them interesting with the new mods. Then the next season will release and give us more mods for a different element or elements.