I come across a lot of stacking and overwriting issues with buffs. As a long time player, but that doesn't get into the nuts and bolts of the game in the kind of detail some do (like knowing what SPA's are, and which belong to which effects), it just gets really annoying at times and hard to figure out. I'll list a few of my annoyances, perhaps others can chime in with theirs. Talisman of Celerity overwriting the longer duration Symbol of Celerity buff from Unit of the Kromrif/Talisman of the Ry'Gorr, even though both are just a straight 60% haste. Shared Cloak of Rimespurs being a single point more DS than Cloak of Rimespurs, so the shared version will block the Cloak of Rimespurs triggered by the combo buff. Cleric spell haste not overwriting lower level versions, so that you can end up with like 3 different versions of them on you taking up buff slots. In general, I also just don't like how stacking issues can block buffs that have multiple effects because of one of those affects being duplicative of some other buff. For instance, Yaulp being blocked by the ranger hp/attack buff. Which means you can't get all of the other benefits of Yaulp because of the +attack conflicting. Was there some reason why buffs in this game couldn't just apply the highest of the effects when multiple buffs are on that do the same thing, rather than blocking the whole spell?
Some spell conflicts are by design, you have to selectively block the stuff you don't want to get the stuff that you do. For example as a Berserker I block mod rods, all the cleric spell hastes & mana regen from enchanters along with Paladin HP buff (& Beastlord hp/atk unless raid has no Rangers). I also block the "voice of X" spell lines from SHD as past experience has taught me those jokers liked to make me pull aggro "for the lulz". If I were not a raider I probably wouldn't put some of those on block. As for Talisman of Celerity, why would you even use that once you have the most recent unity?
Some toons aren't high enough to get the most recent unity, so it would be nice to be able to cast talisman of celerity on a group without worrying about whether it might overwrite the symbol on those that have it. Besides, I don't get why it does overwrite it at all. Seems like it is a bug or otherwise unintended anyway.
Not a bug, and intended as its a limitation of the game engine. The hard stats of a buff can be checked for stacking, not the duration. Probably an artifact of group > single buff, limitation of the engine. By design group buffs are priority over single I believe? That's typical stacking, not sure what the issue is here. I remember it's been brought up but I don't remember a dev ever explaining why there wasn't a stacking SPA created for this, or else it was one of the stupid old design reasons of self management of buffs. Because this game is 20 years old, back then they didn't have the code support for "apply highest of" stacking so everything was written as "overwrite if higher." It has gotten better where they have SPAs now that allow multiple types of a buff to coexist but it only applies the higher value that you have (or they allow stacking of multiple of the same type as the case of crit multipliers). The game was balanced around players only having a max value of X, not multiple stacked values. At this point it would be a huge undertaking to go through all spells to convert them from "overwrite if higher" to "apply highest of" for all available spells (if possible), and with our limitation of number of buff slots it would create more issues with buff slots being taken up.
1. Yep in the end it is the same buff and the game doesn't care about duration. Heck even the level of the player casting it is considered and a lower level cast won't overwrite a higher level one. 2. Yep because as you said the single target is better even it if is just a single point. Best they could do is have the DS match so they would overwrite each other. 3. Yep this is because they are focus effects stacking on that is tricky. For some spells rk3 of the previous expansion is better than rk1 of the current expansion. Your last comment is why they generally don't make a single buff the does everything.
FWIW, you shouldn't need either. Pact of the Wolf AA is all you need. Edit: I guess if you're buffing other groups. Never mind.
Lower ones are fine in house but if you use the top ones sometimes better to block and unblock with a hotbutton though wish they just had a summoned items toggle.