I have to say I'm disappointed by the new DoT durations. I wasn't thrilled with the idea when it was first announced, but I was at least hoping to see some planning behind the durations and uniqueness between builds. Everything going to 20 or 30 seconds is IMO a bad idea, that removes the individual feel of each class and removes the option of full DoT rotations (you would need 20 bar slots).
This could be done so much better, allowing players to choose between micromanaging timers or cast and forget. It could be based around other class skills, allowing things to line up nicely for static rotations (which is not the case currently).
Let's discuss examples. Necromancer is heavily based on casting Blastbones every 3-4s (depending on range). This was always awkward with 10s skills like Wall/Boneyard and the 16s skeleton. Why not make Boneyard 12s so it could align nicely with a casting pattern for either Blastbones timing? Siphon has always been 12s and could remain so, which also worked well with 12s Entropy. Skeletal Arcanist/Archer could become 24s.
Nightblade has a different cadence, based around bow procs every 5th skill. However I've been told that many with high ping or an imperfect weave prefer to cast it every 6th skill. Why not embrace both of these options? This could be a good instance to utilize the 30s DoT timer (divisible by 5 or 6) for skills like Path, Shade and Cripple. This gives a lot of time for casting spammables and executes. Maybe offer a 10 or 20s morph for those that would prefer more timer juggling.
Warden is the one I find most baffling. Shalks has always been a semi-spammable with timing every 3rd skill (much like Blastbones). Why was it converted into a weird 10s "DoT"? Many players like the 3-based rhythm of Warden, and some even like the 6-beat of Subterranean Assault. Why not keep both of these options for Shalks morphs, and plan other timers to be based on multiples of 3 and 6? Winter's Revenge at 12s worked great, but I'm not opposed to it becoming 24s. Extend Fetcher to the same duration as WR. The bear is ready to cast about every 24s so that could also fall into a static rotation, and 24s Netch, Lotus and Frost Cloak would all work well. I don't think the 8s Subterranean with 20-30s DoTs in v8.1.0 is helping anyone.
Sorcerer seems to be having an identity crisis. The Crystal Weapon buffs succeeded in making stam sorc very unique with a strong 2s semi-spammable, as well as one with 4s effective cooldown (Bound Armaments). Changing Crystal to have lower damage and lower cost makes sense, but Armaments was already arguably underperforming. It just did not do much damage compared to similar skills (Blastbones, Merciless Resolve, etc.). I can only imagine reducing the Armaments proc down to typical spammable damage was a mistake, there is no reason to slot it on PTS. If the 2/4 second cadence persists then Stam Sorc could be based around these timers, using 16 or 20 second DoTs. Maybe something like 16s lightning splash + caltrops and 32s hurricane would work.
I haven't mentioned the magicka side of Sorcerer (which is very different than the current stam meta). It has been primarily based on curse timers (either 6s or 12s), with some random Crystal Frag procs mixed in and a dynamic combination of spammables and executes. A multiple of 12 would be ideal for the class DoTs (pet activation and lightning flood or liquid lightning), as well as Boundless Storm going to 36s or possibly 48s.
Templar is an interesting one because it doesn't have a strong driver for timers. Historically it had a lot of 10s DoTs (Blazing, Barrage, Reflective, etc.), but also had some strange timers mixed in like 6s purifying light (or 9s PotL) and 12s Ritual of Retribution. This one could go any number of ways, but I'd lean toward embracing the factor of 10 because it is easy and no other class does this. Blazing could remain 10s or go to 20s. Purifying/PotL could be either 5 or 10, and Ritual could go to 20s.
Dragonknight has also had some strange and mismatched timers. With FoO, Embers, Engulfing, Eruption and sometimes mixing in Stone Giant as a debuff. They have a melee semi-spammable in their toolkit, but rarely use it since casting more whips is typically preferable. This seems like a good candidate for longer DoTs, and is a throwback to the Elf Bane meta. I could see something like Embers and Engulfing being 15s, while FoO and Eruption go to 30s.
Generic skills like Wall of Elements and Blade Cloak can keep 2 duration options, and players could choose whichever fit best with their other skills. Something along the lines of 12s or 20s would fit just about every build.
Obviously these are just examples, I'm not saying they are perfect, but each class would at least feel different. I'd like to see more thought put into the gameplay of each class and synergy between their skills. Slapping a 20s or 30s time on every skill in the game is not good design.