Again, I'll repeat what you seem to not understand. In terms of fads/trends like (E.g. Battle Royale/ Pokemon Go,) Halo started 0.
Next your going to tell me CoD4 didn't start a tReNd with modern military shooters, repeating something over and over doesn't make it true.
Although it started the actually good console shooter trend, in terms of trends like battle royale, Halo started 0.
When I said "Halo doesn't start trends," I don't mean things like forge and theater. Those aren't trends. Those are just features. If we look at any actually trends Halo started, it's 0.Glad we are ignoring all the other ones I mentioned. This isn't a matter of opinion, you are simply incorrect. The phrase "Halo killer" wouldn't have become common place when was a follower.
Denying Halo was ever a trendsetter is ludicrous.
Halo 2 made online console gaming a necessity for triple A games, something PS3 and Wii ensured because of Halo 2 alone, Halo was xbox live.
Halo started the trend of online gaming in most homes, as PC online gaming was still niche and limited at the time, net wasn't great globally. Halo made it popular.
Halo CE made every shooter since put effort into multiplayer because before CE there was only goldeneye and conkers bad fur day that put in real effort on console. Multiplayer became equal to campaign for console shooters because of halo.
Esports as we know it was pioneered by MLG with Halo as the flagship game. Halo was the first to be televised and was the only fps game to stand up against UT, Quake and CS. Halo broke viewership records and made competitive gaming a household name.
Halo popularised streaming and longform game captures as players wanted to see players practice and full tournaments. It dominated youtube gaming from 2005-2009 and was a big factor until 2012.
Every game since has looked to Halo for vehicular gameplay design.
Most Fps games use Halos style of objective gametypes, the 3 big pc games i mentioned inspired Halo, but Halo layed the blueprint for how to do it for all console fps.
Halo 2 set the trend for large scale ranked gameplay.
Halo set the trend of global leaderboards and stat tracking.
Many games were inspired by H2s regenerating health.
Any game that attempts smarter AI uses Halos foundations.
Emphasis on playlist and gametype variety as a vital aspect is due to Halo.
Halo set many standards of fps campaigns, half life with most of the others.
There are many others where if they are not the origin are still either the benchmark / standard of what it should be or modernised / popularised mechanics or features.