Are 6*s still worth the investment?

My account is very weak in the tech class, and I’m tired of waiting to pull a good 7*. Because of this, I’m considering taking up a 6* or two to r4/r5. I have enough dust for 1 ascension and ~150 sigs to put in. Are any of the following 6*s worth the investment? Ghost, red skull, shuri, prowler, ironheart.
For context, I’m a relatively low level valiant and my priorities are battlegrounds and endgame content. Below is a photo with my top 18 champs.

Thanks in advance.
Edit: I forgot to add an option for saving for 7*s. Feel free to write a comment if saving is the best move.
For context, I’m a relatively low level valiant and my priorities are battlegrounds and endgame content. Below is a photo with my top 18 champs.

Thanks in advance.
Edit: I forgot to add an option for saving for 7*s. Feel free to write a comment if saving is the best move.
Are 6*s still worth the investment? 24 votes
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Comments
For example, I'm going to rank up BPCW because his 7* version is not easily available, and he needs high sig to be effective. So a sig 200 6R5A is actually better than an unawakened 7R3. And even if I had the 7, he's not really a good enough champ to justify using an awakening gem or 200 sigs on. At least not right now when those resources are still scarce.
Anyway, in your situation, I think Prowler makes sense. His signature ability is very useful, so if you can max it out as a 6 that would be worth it I think.
I have a r5a ghost. I don't remember the last time I used her. (I do remember tho, I brought her for a war fight few months ago) But she is not getting used.
My alt account has a r4a ghost. I upgrade her for the reason that I'm an old player, I'm comfortable using her and she is 100% nostalgic upgrade.
War showcase R5 tech gem, I gave it to fantman on my alt account today.
I was in your situation. I took redskull r4a and kept him there. Many options I kept at r4a rank. T6cc is not a common commodity for a progressing player.
Strongly suggest to r4a redskull, he is great on attack and helps out in other arenas. Like fighting stupid dominos in random content. Ignore these ghost voters.