Keeper or non-keeper league? If so, what is the cost (if any) of keeping the players? In my league, Holliday would cost a first rounder and Niemann, Guzman would both cost a 20th round pick in next years draft. If the team acquiring Niemann/Guzman were out of contention in a keeper league I would say the trade is fair.
Even without disproportionate costs to keep the players, I wouldn't be totally opposed to it. Then it would really depend on the rest of the rosters. Does the team trading Holliday have some solid bats and OF to be able to absorb the trade? Is their one glaring hole 1B where they are in hopes of Guzman being a long term fixture? Under those scenarios, the trade, while maybe not "fair" would be justified.
In the end, as long as no collusion is occurring, I believe in letting someone make their own mistakes in their keeper leagues.
If not a keeper league, then I totally agree it is an unfair trade.