We already had this discussion in the Grodd forums.
You didn't justify anything of what you said. You just kept saying that Grodd didn't have a way to PROPERLY open someone up with grodd for a combe. You never answered what you meant by PROPERLY. That was some vague justification. People in the Grodd forums answered your question. There are many ways to open people up with Grodd (Staggers, Throws, Whiff punishes, Leaps, vortexes etc) but you just ignored what everyone said.
Now you are asking about credentials? I'm guessing that what you mean by this is again, since I am not a top 8 placer I don't believe what you say. You say you are not sheeple but I can tell that if sonicfox comes and tells you Raphael is the best character in the game you will believe and share it because he has "Credentials"
OK I don't think I was a huge part of THAT discussion in the Grodd forum but the one where you just posted 2 videos and said "Here ya go, Grodd's not so bad" was what I was referring to (Which wasn't in the Grodd forum so my bad, don't remember where it actually was lol). We all looked at them, we talked about them and I shared why I thought these Grodd's were doing well in those videos. I gave my information, I gave my reasoning, and I was basically just using what I was seeing from those videos as my evidence for why I don't think Grodd is that great.
I'm not going to go into that discussion again, but I've said multiple times that taking a top players word as law for a character's placement is a bad idea, but it DOES force you to at least think about it. The same goes for seeing character at top 8. Otherwise we'd think that Flash is low tier still because of HoneyBee, or think Canary is top tier back when Sonic was wrecking with her, or think Darkseid is top 5 because Sonic "thinks so".
I'm just going to summarise my current thoughts on how Grodd plays the game.
I'm ready to be proven wrong. I am so ready right now. I want to be wrong because this character is ducking lit. He has decent stagger pressure with his now mostly negative SC's but that's about it for the neutral. Sets him up for throw loops which is probably the worst throw loop in the game but it's a loop nonetheless, can bait throw techs with B3's etc. Yet to see anyone open people up with it consistently as I see Black Adam and Supermen open people up with it but it's there. Leaps' kinda a bill in the neutral since most characters can just air-to-air it for free, or if they have strong anti-air (Which a lot of characters have at least one) then it's basically just a free combo. It's a counter zoning tool but if you're careful with your zoning and use your tools correctly then there's always a really basically answer for it.
His vortex(s) are actually super legit and scary but kinda overshadowed at his ability at getting them started (Which is a problem he has had since the game came out and has been buff/nerfed since then so it's hard to say whether he's slightly better or slightly worse). His D1 is the best in the game as a punisher and for poking out of normally pseudo plus frames like when Supermen do F23xxBreath -> F2 (Super gimmicky example I know but hopefully that makes sense). His D2 is strong. His damage is amazing. Wakeup game is good. D1 combo starter in trait. Good jump ins even though his jump is floaty still despite the recent buff.
I just don't see how anyone's getting opened up by a character with the tools mentioned.