So when it comes to JYPE and solo promotions the favourite phrase from kpop/Twice fans is "they don't want another Miss A" and for me this reason has barely ever held, so the fact that it keeps getting regurgitated with no-one thinking about it is odd to me.
You look through the career of the Miss A members and most got solo promotions, some even more than Suzy pre-debut. People only seem to remember Suzy's just because of her blowing up post Architecture 101 so ended up with the biggest/best opportunities (and within spaces kpop fans know more about like kdramas) but even JYPE will know how much of an anomaly she was. You could argue only Lee Hyori had a higher peak than her in terms of female It girls from kpop in SK.
Miss A never had good sales. Suzy blowing up like she did made her more valuable than the group as she bought in huge CF's ("10 billion won girl"). She on her own ended up being more valuable than Miss A as a group probably would have ever been. Sucks for the other members but why would that be a bad thing for the company, especially when female solos had a better record in the long run? During the early/mid 2010's when JYPE were struggling the articles out would always mention how she was one of the keys to saving the company in a way Miss A as a group probably would have never done.
Suzy blowing up was not detrimental to the company.
You then go onto Twice. They didn't have a massive start but Tzuyu was very popular with the public, JYP/JYPE all knew this. If they were so worried about what happened with Suzy why on earth would they push Tzuyu like they did in the first few months? if the flag incident didn't happen how much more of a push does she get, especially with the allure of China money which I have no doubt was heavy on the mind of the company? If Tzuyu solo is making a lot of money and more than the group that is what they'll push with the group being more one and off like Miss A were.
But then the flag scandal happens stopping any further investment into Twice's most popular asset at the time (which was a solo Tzuyu) and Twice get massive off Cheer Up. That's Twice the group. Now Tzuyu is no longer the most valuable asset, the group is and they were also big enough to now get big group endorsements. From Cheer Up onwards the rest is history. JYPE needed money, Twice the group were now incredibly popular so they pumped out release after release for years. Twice in their first 2/3 years had no time to do solo stuff as the company had a guaranteed and safe income source in group releases, especially after blowing up in Japan as well so the opportunity cost was barely considered.
They weren't ignoring solos because of Miss A/Suzy, they were just a much better, higher margin, less effort money machine as a group. Why would they pause activities for 2/3 months to build solos at a point when they need money? Why would the company take that risk? Twice didn't have the luxury of the company being in a state to think in the long term for them with regards to their careers (or their health).
Twice fostered the idea of how much money a group purely doing group activities can make (in the 2nd gen solo activities within groups thrived) and as the first ones in the new division system at JYPE in 2015, they specialised within that and found it massively profitable. JYPE are now consistently rocking large margins following that same path.
JYPE getting rid of their acting divisions/all their soloists leaving is also another example of how the approach to JYPE groups has nothing to do with Miss A but more so a general shift in the attitudes of the company coming off the success of Twice and a lack of solo success after Suzy left (and Taecyeon). They weren't particularly good at those things regardless, with Suzy being a massive anomaly and the most in demand star around. Sunmi and Baek Yerin both became bigger soon after leaving JYPE. They couldn't do squat for soloists but were faring good with groups so it took over the agenda. Not because of Miss A. Only now that they have the means again to expand and experiment you're seeing some of the newer groups branching out more as they can afford to be less risk averse.
For me, Twice still don't do any now as they spent so long needing to be a group for the company that they now only have a year left and until members start committing to renewals it doesn't make sense for the company to do it. As much as I want it for multiple reasons if I'm JYPE I wouldn't be spending money/time/effort building up Twice's solo relevance unless said member was committed to staying and therefore I'll be reaping the benefits in the long run. The groups success is at a level still where there's no need for them to take that risk yet.
JYPE's revenue diversification is poor compared to the other big entertainment companies so they need groups to provide a consistent income stream so will always take less risks outside of the safe zone that is group promotions for them now.
Long story short - Suzy blowing up probably ended up being one of the things that saved JYPE. Twice didn't do solos because the group was more profitable post-Cheer Up. Imo, now it's too late in their careers to properly start it back up unless members start committing to renewals (/ask for it). I don't think Miss A has anything to do with how Twice/other JYPE groups are promoted, it's down to circumstance and what ended up more profitable for the company who then specialised and played to their new strengths.