What I miss about Haga is the longer term strategic play that it brought to SAM as a class. You wanted to keep it on cooldown, but not always immediately. Maybe it was better to use it right away so it was ready again ASAP, but maybe you delayed it for a few GCD's to get another 20-40 kenki from it. Which was best depended on the situation, and you could selectively use it to enable mechanics to be dealt with easier (such as being forced onto a flank to dodge aoe and eating Ka so that you just run through your Kasha combo again).

What I don't miss about Haga is that - outside of raid bursts windows - you wanted to more or less keep it on cooldown. The gain almost always outweighed what you got from using Sen on anything but a Banana refresh, and even inside burst windows it wasn't always a clear cut win for Midare; sometimes you needed to be mobile, so Haga would win out since you could spam more Shinten's.
I like that Haga is back now, and it still has limited in-combat usage depending on your circumstances, but I also like not using Shinten so much. It's not a bad skill per se, it's just not very interesting. Push button, receive damage. Keep your kenki gauge above a certain level so you can use Kaiten as needed or Guren/Senei when they start to come off CD, and even that isn't a challenge now with Ikishoten lining up perfectly with Guren/Senei. So while Haga allowed an interesting style of play that I came to love with SAM, it also paradoxically imposed it's own dogma onto the class. You wanted it on CD as much as possible, and waiting more than 2-3 GCD's to put it on CD was pushing into lost dps territory.

There are other ways to increase SAM dps. I'm fine with Haga as it is now. It still has niche in-combat use, it's just not required to be used like it used to be. It's an option, not a requirement, and that's a good thing.

Specifically on the topic of boosting SAM dps, I like the idea of Kaeshi: Banana double up with normal Banana on an enemy, but you'd have to drop the CD of Kaeshi probably to 30s or else all you're going to use it on is Banana. SAM needs more overall options not less, and no, more Shinten spam is not an option it needs. I'd like to see more conditional stuff beyond the minor niche stuff current Haga brings. To be honest, I think the Kaeshi's are an untapped option. I'd love to see a 30s CD on Tsubame-Gaeshi with each different Kaeshi granting SAM a personal buff of some sort. Kaeshi: Goken could add a 15s buff that increases the potency of all aoe skills by 10%. Kaeshi: Higanbana could cause the SAM to deal an additional X amount of potency for every AA and weaponskill used on the target for the duration, maybe something small like 10 or 15. Kaeshi: Setsugekka could grant three charges that increase the damage of the next kenki spenders by 25%. These are all obviously just suggestions and ideas, but I'm sure everyone gets the gist; let's add something personal and defining to what's arguably the best SAM skill added in this xpac. Something unique that has a noticeable effect but also introduces a measure of decision making that goes beyond "use this on cooldown."