First off, fantastic work with the game. I left a 5* rating already, and hope to see continued work on this in the future. This is already impressive enough as it is since you're a solo dev, and I certainly don't want to take that away from you. Now, lots of other people have left feedback on many systems, and I haven't quite had the time to go through all of the posts so apologies if some of this is repeated.
The first thing that I've seen others comment that I'd like to also bring up is the economy. In a lot of ways, gold should be king, but I feel like it solves way too many problems way too easily without enough drawbacks - AND it's too easy to come by without enough late game sinks for the funds. I didn't even have to worry about finances in my first season with the hardest start. I was able to immediately snap up all the best recruits - and even a Mythic Loremaster - and immediately make up for the increased expenditure with delves. Again, I do believe gold should be king, but right now there isn't much need for creative strategizing as by the end of your first or second season you'll have enough funds to simply brute force through every obstacle with money. I think one of the ways this could be fixed is by using guild tier/renown as a factor in recruitment. Either the current ratings of adventurers that will show up in the tavern will be adjusted OR have a contract negotiation system wherein a lower tier/renown guild may have to pay more to convince higher rated adventurers to join.
The second thing that I want to bring up that I didn't notice anyone else comment on is the development system. The reason no one else has noticed this likely has to do with the prior - where development isn't really necessary since you can always afford the best recruits. Regardless, I decided to dedicate a roster/training slot to train/hone an early 4* prodigy, and by the time I was 5 seasons in, he had only gone up 12 or so rating points - going from ~48 to 60. This isn't really meaningful in the grand scheme of things, especially when paired with the prior point. For most start-of-game and recruited prodigies, their wages will tend to be around the 17-25g range (worse if they have Greedy). When you consider that most of the 80+ rated recruits have wages around the 25-45 range, these savings don't really make much sense - especially after renewing contracts and having their wages go up as I'm developing them. I want to be rewarded for being loyal to recruits that I raised myself - either by saving absurd amounts on them and/or by being able to turn them into legends within a reasonable amount of time.
The third thing I noticed is the brute-forceable nature of many of the dungeons. When you have a full 90+ rated party (or even 80+ with one or two 95+), it almost doesn't matter what your comp is, how they're spec'd, or the modifiers. I'd basically just select my A Team, give them all of my best available gear, and let them go. I'll grant that I finished my last save right as I was promoted to the top division, so perhaps the delves would have been much more difficult there, but even so I typically only needed to change a gear piece on one unit for a modifier (typically: Tank for Flooded, Melee DPS for Cold, Range DPS for Blind, and Healer for Cursed - if I'm remembering each of those effects correctly). It also felt like I never needed to diverge from the standard tank-healer-2 dps composition, which felt a bit odd since synergies like Phalanx existed. I'd like to have to strategize a bit more - whether in gear, composition, or both - AND I want underdog teams to be able to challenge more difficult dungeons by having the correct mix of gear and composition. I may just not have experimented with this system enough to really see these differences, but at least at a glance it felt that way.
I'd also like to touch on the "spec" part of the prior point a bit. In Football Manager, for example, I can have a Forward/Striker, but how this player actually manifests/plays can be entirely different based on how he's spec'd. He could be a Complete Forward, a Target Man, an Advanced Forward, etc. Alongside this, while a player may be a 70 or 75 on the 0-99 scale, if his specs are so perfectly fit for a role, I could win a UCL with him by having him be a complete system player. Taking this back to Dungeons & Dynasties, I feel like it doesn't really matter how I spec a unit. A glass cannon Blademaster doesn't really feel any different from a tanky one, a balanced one, a crit-focused one, etc. On top of that, no matter how I build one, pure rating is still what ends up mattering most - and I'm unable to do the same sort of "plucky underdog system player" strat that I can do in FM.
All in all, my feedback basically boils down to: I want the economy to be more meaningfully challenging so that I can play a more development-focused style, yet still be able to punch above my weight class through precise strategies and builds. Again, the game is fantastic and I had a blast with it, so I hope my feedback didn't sound too harsh.
P.S. in line with my development-focused suggestions, I think it could also be cool to have a reward for underdogs clearing a difficult delve by boosting their stats past their initial limits. Essentially giving them a kind of "awakening" that lets them ascend to another tier. I personally just really like watching units I've invested in become really strong. Maybe I've read too much isekai/system/tower manga/manhwa (like Pick Me Up! Infinite Gacha) or played too much Guildrun recently haha.
P.P.S. Being able to customize the crest manually rather than randomly generating it would also be nice.