To answer the question - if you're not going to hoard up to get three 13-cover 5*s, then IMO you might as well go with 5* Kitty Pryde. She's pretty nasty.
If you do have a 5 yellow cover Grocket my advice would be you better treat it as a really big gamble and resolve yourself to understanding you're giving up a lot for a very low chance of getting an effective Kitty and live with the consequences that RNG may be unkind to you. It's your call on whether the risk is worth it. To me, personally, I'd rather build up my 4* roster because champing 2*s,3*s and 4*s give you other resources that help you further progress in the game. Even a 1 or 2 yellow covered Kitty, to me, wouldn't be worth giving up all those possible resources/rewards.
Also, in PVP, SCL only matters for rewards. You still get hit by the same people. It's not a measure of difficulty (just in case you thought it was). PVE on the other hand SCL is difficulty level (and better prizes).Additionally, if you're talking about character PVP (vs SHIELD Sim), you only get to chose 2 characters plus essential, so your 3*Daken team only works when it's his event. The main problem with running a Champed Kitty is that her level would be such an anomaly to your current character levels. She'd be 450+, Grocket at 140ish, and whatever 3* boosted (~260). Your team would be a big target since you'd basically be playing 1 on 3 vs stronger rosters. Also, you'd kinda be stuck using Kitty on every team, and she only excels with certain teammates.
I really need to learn how to read one day I thought you were trying to champ out Kitty. Anywho, at this point your biggest issue will be HP for roster slots. That's one of the reasons not to open LT/spend CP until you're ready. By the time you're ready to be a full on 4* player or 5*, chances are there'll be another 5* that'll be worth chasing.If you want the Kitty-lite experience, bonus hero Nico. Once Kitty leaves latest legends, it'll be easier to get bonus Nico's over Kitty...
I was in your same position 5 months ago when Okoye was the hottest thing. First, I want to say that you're doing very well! After 11 weeks from my restart, I had 20 x 3* Champs and 70 LL pulls, which is about where you are. It sounds like you're struggling for roster slots, like I did. 4* covers are precious and you don't want to waste them. So, if you pull now and don't buy HP to roster everyone, many will be wasted. Kitty should be in Latest through the end of this upcoming season. I would expect her to leave either on 2/18 or 2/25. So, that gives you 1 or 2 more weeks than you're expecting. With 105 pulls, the odds say that you should get 5 Kitty covers and about 4 x 4* BH. I've looked at your gamependium roster (assuming it's up to date) and you don't have Grocket or Blade or Carnage or Clagger rostered, and Medusa has 1 cover. Theoretically, you could get a 2/2/1 Kitty and a 2/2/1 Grocket, but that still isn't good enough to fight with. So Gritty isn't an option for you right now. You could BH Carnage instead; all you need is 1 black cover, and then pair him with Kitty. At low levels, it's not a killer team, but it could work. There is, of course, inherent risk with that plan as luck may not go your way. Kitty is the key though. If you get 1 or 2 yellow Kitty covers, then you could pair her with 3*Daken / 3*Blade / 3*Fist, which you do have fully covered. But to make Kitty effective, you would need to level her up as much as possible. To answer your question about opening your hoard or not......I did not when I was in your position. I knew Okoye was great, but I would rather have 3 fully covered 5* in the future, than a half-covered great one now. I waited until I had 200 pulls and a top tier 5* was in Latest. That was at week 23. I would have liked to hoard longer, but my 4* progression was stalled and I knew Kitty was awesome. Waiting was definitely the best decision, plus I wanted to finish champing the 3* tier before building the 4* tier. If I were you, I would stay the course champing 3*s, rostering 4*s and hoarding LL pulls. I understand well that this period in the 3* tier feels slow and difficult, but your hard work will pay off in the future. Soon enough we'll get another 5* that's worth breaking a hoard for. To answer your other question about MMR, you need to understand that MMR takes into account the boost list for the week. So, your boosted champed 3*s are near the same level as non-boosted 4* champs. That's why you see them regularly in PVP. Opening a hoard isn't going to change that either. What will change your MMR is getting some 5*s and leveling them up to 350 or champing some 4*s and then they get boosted for the week. That's when you'll face boosted 4* champ teams instead. For now, bring your best 3* teams to the table and take down those 4* champs. I liked IM40 and Strange. My backup team was Cage and Fist.