Picard I think you gotta define what exactly you mean by "soft".
I understand what you mean by risk taking... There's stupid risks, and smart risks. Smart risks are examples like business ventures that have the potential to yield great profits, etc. Dumb risks are the kinds of stuff I did when I was single: unprotected sex w/ different girls, lotsa recreational drug use, etc. I'm naturally quite hedonistic; I enjoy sexual variety, various recreational drugs and when I was younger I had rather low impulse control.
Soft to me means becoming complacent, and losing the drive for self-improvement. Soft dudes let themselves go physically, career-wise as well as socially... Although a dude can become soft in an LTR/marriage, there are many instances where it doesn't have to end up that way. I think the key is the kind of girl he's with and the nature of their relationship.
Personally for me, there have been some areas of my life where I have improved a lot since starting my LTR, but other areas where I have become "soft" as per the above definition. My physique was definitely getting softer after I finished by stripping career... its tough to train and stay lean when you have no accountability... My fiance totally called me out on it, and I'm glad she did as it drove me start competing in bodybuilding. I've put on around 20 lbs of lean mass since I started bulking: sitting at 5'8" - 190 lbs and still wear 32" waist pants. We're both competitive physique athletes. This is an instance where I definitely haven't gotten softer. Similarly, since I've stopped smoking pot, doing party drugs, etc, I've really been able to focus more on my career. Again another area where being in a relationship has helped me. I'm not the greatest at disciplining myself, and being in a committed relationship to a good girl helps me stay accountable for my actions.
My social network has atrophied since getting hooked up. Girls that I was friends with before, who wanted action from me, slowly stopped contacting me. Similarly, I wasn't partying as much with my friends who do drugs, etc. I suppose this is an area where I have become softer.
I suppose you could say that I'm "soft" naturally when it comes to disciplining myself unless I have something/someone to be accountable to. The key is to know that this is a weakness and find a solution for it... which I did. I've been in an LTR for 4 years now and couldn't be happier.
I think LTRs/marriages can make you complacent if you let them. It depends on the quality of the girl and the nature of the relationship. However, if you're focused on constantly improving yourself being in a relationship may actually help, provided that the girl is quality and supportive of your efforts. Being in a relationship with a good girl gives you accountability, which is what "bad/soft" guys like me really need. You also don't waste time chasing after poonani, so this is more time you can use for yourself. Ideally, I like to think of a relationship as a complementary mutualistic interaction between two people where both parties benefit and become better people. This is what my relationship is like.