I personally think Capricorn is overrated and very insecure and weak but likes to look and act tough by armoring themselves with achievement and status. They're not confident in relationships and good luck getting any of them (even Cap Mars) to work with you where they aren't in it totally for themselves and how great it'll look for their image. There are plenty of Cap people who have fallen into bad and hardcore habits of drugs and indulgent in self-destructive routines.
Scorpio is very overrated but they're "weak" in that they're overly emotional about everything and want to seek revenge when they feel like others have slighted them in some way, even if it's not true. They push people away hoping that the ones they push away will come back and want them and when that doesn't happen, they get even more outraged. Playing psychological mind games and being indirect with further adds more troubles to the table. At the end of the day, they shoot themselves in the foot and hold grudges until their hair turns grey, but the world won't bend to their wills.
I don't really think Cancer and Pisces are "weak," as so much as they drastically crave love and approval from others. Those are not weak traits, as I find those to be very caring and loving signs in most planetary positions. Pisces is forgiving and it's easier to be forgiving and get passed difficulties than to it is to drag out disagreements. Also, Pisces would rather suffer for others than to have it inflicted on others... which can weaken them if they suffer too much for others. The downside is Pisces can get psycho if pushed too far. Just encounter any Pisces Moon and you'll know what I'm talking about. Most Cancer positions are soft and caring and have desires to take care of others. Cancer wants others to return the favor and take care of them, which is why they do try to take care of others. If you use them and mistreat them, watch out! Cancer Sun is #1 sign for murderers. It's very personal for them.
With the exception of Saturn, I do think Libra positions are weak and needs to go on wilderness trips to learn how to be more confident and decisive. It seems strange but I'm finding more and more dictators with Libra Saturn. I think that because of the exalted position, it can make the native feel confident in controlling other people via social measures (such as Putin).
Gemini isn't traditionally touted as "strong" nor is considered to be "weak," either. For the most part, Gemini positions don't place emphasize the personal, but rather, the social. Gemini likes to give off the appearance of agreeing with all sides because there's the strong ability to find validity on all sides but no one really know whats a Gemini really believes and that's something they like to keep to themselves. Unlike Libra, Gemini does NOT fight for both sides. Gemini actually have an easy time making decisions and will pick a side and will fight for that side but if validity for the side they fought for no longer holds true, Gemini will have no problems detaching and jumping ship. That's not really a weak point... as there's more practicality to pick battles judiciously.
As far who I vote for being the weakest, I would say Sagittarius. They're lucky but psychotic and demagogues and just go along with whatever is fashionable. They run away from battles and don't care what consequences their actions bring to others. Not often do others come up as part of the equation. They're only concerned about themselves and do whatever they want to do, so to h3ll with everything else! Yuck. Such recklessness through and through.
Aries, however, I find to be truly tough and strong willed. Despite adversary, they will keep on believing in themselves and strive to succeed. Their selfishness does them credit as they take care of themselves and don't pose as a problem for other people, which I find to be quite pleasant. I can get annoyed with Aries positions because of the over confidence but I've not met a person with Aries energy, other than yucky Aries Moon, to be a drain on other people. Aries is truly independent and operate optimally as 1, which is why they're the 1st in the zodiac.