You need to include a bit more details as an example.
Paragon chests are just a bonus from doing Emissary caches.
I am 100% certain that you do not have every single legendary available to your class.
You would also need to take into account doing Order Hall rep missions.
If you are hunting a specific faction mount, then doing all the WQ's in a zone daily is time-consuming, but if you are using the 3 day time limit effectively.
You are only doing 1 or 2 super fast WQ's in day, maybe 0, if there is nothing.
Eg. (Today is Warden's and yesterday was HM. There were no Warden WQ's in HM so there was no reason for me to do a single WQ)
If you take into account travel time to said raid. Depending on the raids location... In most cases.
You can complete all the easy WQ's before even getting to the Boss mount that you have on farm.
You also did not mention if it was a full clear or a saved lock.
Overall, I would say that quick and easy WQ's(Warden's and Kirin Tor) are way more efficient than farming a boss mount that has 5x less likely chance of dropping.
If you could give me a more specific example/comparison.
I would have a better understanding.
Note: I have opened 320+ Paragon Caches, 2400+ Emissary caches and 1500+ Legionfall recompenses as well as have a lot of rare mounts.
So I do have experience in both aspects.