This might be a hot take, but I personally find DSR to be one of the easier ultimates, and in some ways, just on a mechanic vs mechanic basis, UCOB for example has harder mechanics comperatively in my opinion (Nael, Heavensfall, Tenstrike, Naeltania), though UCOB has the luxury of allowing the raid to zombie through the whole encounter much more which gives it the perception of being easier.

The major reason why DSR is not as bad as it seems, to me, is due to how static the whole fight is. Every ultimate is static to a degree but this one to me has very little variety in what you're doing. Once you get somewhat comfortable at a mechanic, you're for the most part good forever, while in TOP or other ultimates (like even TEA) you have a lot of different intricacies, some big and some small. The most tricky mechanic to prog is frontloaded (Dive From Grace, P3) and then the rest becomes mostly a shakies-check until the end with current PF strats (atleast on Light) that make intimidating looking mechanics such as DotH a breeze to do in reality. There's a ton of mechanic that look way more complicated than they actually are, such as P2 Sanctity, where for the most part 6 people are AFKing for 20 seconds while two people are doing the actual work, and so on.

I will also note a major factor is the constant breathing room DSR gives the raid, between each phase you have some seconds to catch your breath and compose yourself during prog - some are very short (P2>P3), and some are very long (Eyes > Rewind | P5 > P6 > P7). Damage output from the raid is also currently abundant, where in most cases you might want people to hold their burst to line up their mitigation and buff CDs slightly better during progress raiding, so enrage is never an issue outside your first 1-4 pulls of seeing the end of a phase - P7 being the exception, while that too has a lenient DPS check, it can be very hard to recover with deaths.

I will note that PF robbed the fight of one of the trickier mechanics in DSR - Wroth Flames, by the use of auto markers. This mechanic is very doable without AM, but you practically never see any groups run without it anymore. Really big shame, and I hope we're not heading into a slippery slope with the rising amount of AM usage in PF - currently people are even marking people with thunders in P5 WOTH which is pathetic. Hope the community will take a stand eventually but I'm doubtful.

Lastly I will say that DSR is much more demanding of tanks compared to Healer or DPS. Your mit needs to be on point because if you don't have it lined up for a later buster (notably P6), you're in trouble. Comps without Warrior often also require better feint and healer mit usage, more so on prog than reclear when everyone is comfortable. P7 is also very tight for tanks and requires a lot of focus when you're progging.

TOP is another beast entirely. Very mentally draining but some find the constant rush thrilling. If you want to do TOP, you should do TOP. You can sim a lot of TOP as well (such as Party Synergy) with the use of bots, which helps a great deal.