Other than glory packs you mean? Frequently collecting tributes for glory and spending it on several troop packs per week is by far the easiest way to collect every arcane you need and then stay ahead of new troop releases in perpetuity.
Dungeon Gem Bounties are decidedly bad for hunting arcane trait stones. To get the extra resources for one extra celestial, you need to spend gems on every day Monday-Saturday. This is 300 gems. One celestial gets you half way to crafting an arcane of your choice. In my experience, double-arcane is close to a 40% drop chance from a single VIP chest, or 300 gems gets you an average of 4.8. Celestial seems to be below 10%, but you shouldn’t bottleneck on those unless you are using them to craft arcanes (I recommend not doing this, you’ll need far too many Celestials to get usable amounts of arcanes that you’ll end up running out).
Gem keys I’m estimating at about 5% chance of arcane (because VIP drop double when they drop), so gem keys will get you less total than VIP, so your gems should not go to gem chests. Glory used to glory keys is at least worse arcane returns than just buying the glory packs, so don’t do that, either.
Gem Bounties on Monday-Saturday are pretty bad overall, whether you are going for summoning stones or celestials. You are exchanging 50 gems for 24 diamonds (if you craft the shards into diamonds). 8350 gems spent this way will get you 4008 diamonds for a mythic of your choice (and 2800 of each jewel, or about 28 celestials, or 14 arcanes to craft) after about 28 weeks. 8350 gems spent on VIP chests gets you over 180 pulls, which I’m estimating at 140+ arcanes, at least a handful of celestials (and some legendaries and epics). You also have that mythic chance, estimated at 1% per pull and on an exclusive week, it will always be one you need. At 180 pulls, you’ll average 1.8 mythics, or have a cumulative probability of about 83% to pull at least 1. Used with the correct timing, you’ll get far more mileage out of your VIP keys than you’ll ever get with these gem packs. Again, I should bring up that you have put down thousands of gems and waited 28 weeks to put all these Jewels toward celestials toward arcanes and you still don’t have enough to trait a single legendary.
The Sunday Gem Bounty offer is a much better deal in all regards, netting you a celestial by itself for 50 gems as well as 84 diamonds and a couple gem keys. Looking at it for arcane hunting, that is one arcane you can craft right there of your choice (again, wouldn’t recommend for general use). Extending long term, 2400 gems spent this way will get you 4032 diamonds over 48 weeks for a mythic of your choice (and 96 gem keys, 48 celestial which can be crafted into 24 arcanes.) The gem keys will net you a few more arcane. The same gems will get you about 53 VIP pulls, or 40+ arcanes and a few celestials (along with the troops). 53 pulls will get on you average 0.53 mythics, or has a cumulative probability of 41.3% of pulling at least one. So Sunday’s Gem Bounty pack is still worse than VIP for arcanes, but much better than even VIP for mythics. Worth buying regardless IMO, it just won’t further your arcanes goal much.
Also, as you can see, these packs would take a great deal of time to make any impact on your arcane count.
To get any usable quantity of the one you want outside of glory packs, I’m afraid the only viable way is still Explore. The second most viable after that is glory farming/hoarding and paying attention to the spoiler thread to plan out what you actually want, which is still faster than trying to get them through crafting or shotgunning through PvP. They are about 1 in 50 from non-explore battles and treasure hunt, so these don’t usually net you usable quantities especially when they are also then split another 21 ways via various colors.