You are so RIGHT RIGHT RIGHT! Strong male leading fathers are SOOOO important. And sadly, a bit of a lost art.
All I can tell you, is that I can give you tons of examples both ways of Strong Disciplinarian Fathers vs Mr Nice Guys, and hands down, the Strong dads win. Of course they need their fun loving soft side, and not to be angry abusive people, but that strength as a leader is SO important in the home! And to the security of the kids.
For the boys, they learn to harness their hormones, follow the rules, be little gentlemen as well as be tough, and be strong leaders when it's their turn. For the girls, they learn to find a strong man in the future and to trust their dad's word, not sucker him into stuff all the time. Like both parents, he should be a fun loving good guy most of the time, and the final word on discipline when necessary. The kids NEED him to make the boundaries clear.
I have some sensitive male friends who are amazing kind people, and really fun playmates to their kids, but have no interest in being the bad guy ever. As the kids get older, they are unbearable, and they treat their parents really badly. My family on my mom's side, conversely, has really strong males who would never shirk their duty as the last word, and their kids are so much more mature and well behaved.
My softie uncle and hippy wife raised their kids with waffly positive discipline, and as adults, both my cousins have drug addictions, long histories in rehabs, can't hold jobs, can't be accountable for anything, and hate their parents. It's so sad, because my uncle is SO NICE and such a good person, he's a therapist who helps many needy people, but his kids hate him! He always sacrificed so much for them, and now they won't speak to him. They are totally self absorbed. These are extremes, but the seeds of truth are there, which you know, since you already feel your husband needs to be stronger.
I am SO fortunate that my husband is strong and was raised strictly. He does not hesitate to lay down the law and implement consequences immediately for things (sometimes I have to tell him to be a little more tolerant when kids are tired, etc). He's also a big teddy bear and the sweetest guy in the world, so my kids have all the affection they need, the funnest dad at the park, etc. But wrong behaviors are never even attempted around him (more than once or twice). My son is only 16 months, and he already tries to act tough and impress his dad by not fussing etc.
Ironically, my husband is gone ALL THE TIME touring as a musician. So in reality, the discipline is my job, and I'm the primary disciplinarian. However, when he is home, I (appear to) defer to him and let him (pretend to) lead. When I feel he is too quick to implement a consequence, I'll keep quiet, and pull him aside later and explain I usually give warnings first, or that they hadn't been taught this or that, but we NEVER contradict each other in front of the kids, and both our words are final. We always uphold the ruling of the other. But he's the "king". No feeling guilty and being a pushover just because he's been gone for months. He's always strong. Which my kids respect.
I want my son to be strong, and my daughter to recognize a wimp when she sees O. when she gets older so she doesn't have some of the struggles I had (dating wimps in the past, running myself ragged, wearing the pants, and thank god I didn't marry them).
The hard part is that nice guys are so NICE! Your husband is amazing for all the reasons he's amazing, and those are his golden qualities, but he needs to understand that he doesn't lose credibility or likableness with increased toughness, he gains it! Kids love a strong man! Even our friend's kids try to impress my husband, because they know he's a tough guy who is only fun when people are behaving nicely.
People love well disciplined kids. Everyone benefits if he can make it a goal not to waffle! My kids hardly need discipline, because they're never allowed to get away with stuff. If your husband is firm and decisive at the onset of things, they won't escalate, and he can avoid the discomfort of meltdowns or whatever he's afraid of.
So, have a talk with him, see if he can change, or at least understand where you're coming from. Get to the bottom of WHY its hard for him to draw the hard line. See if he can understand the reason to improve in that area. Compliment all his strengths and don't be judgemental as you bring up examples. Also, treat him as if he's already being strong. Don't ever contradict him etc. Tell your kids to listen to their dad and act as if you know he'll do the right thing. Let him feel the fruits of your praise when he's tough O. step at a time. Seek help on how to toughen him up...this is a hard O..
I know when I sometimes have to enforce rules, I just don't want to. I don't want to see anyone cry or be disappointed, I want to be fun all the time. But we have made a commitment to strictness knowing it's for their best interest even if it's not always fun or easy for us. See if you can get this through to him. Most men I know-including mine-look to their wife to direct them in their discipline style. If you know what is needed, you can probably get him to comply with enough work. Most of the guys I know who waffle, are totally allowed to by their wives. Women are secretly in charge. Use your power!