I already broke Grimm, Sonya and Nordri. I use them all the time and the fact that they are limit broken and in one team gives me lots of advantage everywhere.
However I only play with 4*, with heavy accent on S1 4*.
My personal vision is that it’s way better to break a team of 4* rather than one 5*.
So from my point of view all good S1 4* are worthy of ascending, some like Scarlett even in multiples. But the worthiest IMO aren’t the healers, but rather the hitters. For example, I do have cKiril, but I prioritized Sonya and Grimm over him. cKiril’s special ability doesn’t benefit from the hero being Limit Broken, whereas Sonya and Grimm’s offensive abilities are solidly boosted.
4* are not in the consideration for any nerf, which might be the case with some 5*, especially when they are limit broken and seen as way too overpowered. It would be really nasty for all of you when you decide to break your Cobalt and then he suddenly gets nerfed for example…
Plus it’s a really good investment to use LB 4* to give you the edge in upcoming 4* tournaments to get better scores, which will give more Aethers as a payoff. Also they give the edge in Epic challenge events for better scores.
Also 4* don’t consume any 5* Limit Breakers so if I want to break any 5* in the distant future, I will still have the most important ingredient since I presume 4* and 3* would be much easier to obtain.
Edit: Be on the lookout for hidden level-up post-breaking costs. For example, Grimm required a Battle Manual in addition to the food and iron for levels 72-73 and 73-74. It’s possible he required one for the earlier levels and I didn’t notice. But I guess the requirement for leveling a Limit Broken 5* will be an unfarmable mat for each level post 80.