While I think your proposed CP requirements in Modern are about 50% too low, I think you've put together a great argument for the league locks portion.
RE Part 2: Decoupling from tournaments
I wouldn't say the previously implemented restrictions were a failed measure, but they do still have their flaws. I agree with points 1 and 2, however, it gets a little murky around points 3 and 4. Yes, cards owned by Champ players are limited to the league of the tournament and yes, the meta is different in lower leagues, but a quick look at tournaments results down there will show you that doesn't seem to be much of a problem for them.
First, you can't ignore the significant card advantage they bring with their collections. Yes, other players could rent those cards to lessen the advantage, but in a lot of cases, that's just not financially reasonable if you're hoping to come out ahead.
Second, even though the meta is different, that doesn't seem to make much of a difference. We constantly see Diamond and Champ players dominating Bronze and Silver tournaments. Some of it is due to the card advantage that comes with having a larger collection and some of it is skill.
I can't speak much on point 5 because I don't pay attention to the number of entries in Novice, Gold and Diamond tournaments, but I can say that both Bronze and Silver tournaments still manage a pretty good amount of players.
I've always been a fan of the "one up, one down" idea for tournaments and I think that could still work well in conjunction with your league lock proposal, but there would still be a couple things that would need to be addressed. One up, one down would function exactly as it sounds. you can enter tournaments one league up or one league down from your chosen league. Being that Diamond and Champ players wouldn't be allowed to enter Bronze or Silver tournaments anymore, the number of Diamond tournaments would need to be increased, and even though the card levels are the same between Diamond and Champ, I also think some Champ tournaments created.
Thank you for your feedback! I agree that it is an imperfect solution in regards to the tournaments, but even you say in your reply "We constantly see Diamond and Champ players dominating Bronze and Silver tournaments" so the present system has not been effective even in its current implementation. Removing this barrier, even temporarily while something better is developed, would allow league lock to at least be put into place. At that point perhaps the entire system can be reviewed, or the tournament discussion presently ongoing would have a better idea how to solve that issue. As it is now, I don't feel it has any value. There was a lot of resistance to league lock because of the fact that it lessened the tournaments one could enter, so I feel like removing those barriers altogether would allow us to take a fresh look at everything and see the leaderboards and participation rates again in a free and open environment to properly reevaluate. We may just have the same people continue to do what they've always done because I feel like if someone really wanted to play in "all the tournaments" right now, they could, regardless of the 1 up 1 down barrier. Thanks again for the reply, Torran!
I should've clarified better. We see them constantly dominating in tournaments that either don't impose an increased entry, the increased fee pales in comparison to the payouts, or they're inactive in the format (Modern/Wild) that they're entering.
There's also a loophole that's exploited quite frequently, or at least it used to be before the ban on bots in Modern and people started playing more on that side there instead of Wild. I've been a bit busy lately so I haven't paid much attention to it lately, but basically what was happening though, is we'd see players playing Wild, but not playing in Modern. This would give them an extremely low rating in Modern while their rating in Wild would put them in Diamond or Champ. Due to their low rating in Modern, and the increased fees being rating and format dependent, they weren't being hit with increased entry fees. This worked out well for them because it was giving them access to most of the tournaments in Modern and because the Wild tournaments rarely have an increased entry penalty, they were having almost full access to those as well. It did cut down on the number of people smurfing, but it's still pretty common.
I do agree that this is going to be the main argument against any type of league lock. It's a shame that the one person that really seemed to care about fixing all of this was let go. I also agree that there's likely ways to get around a one up, one down type format, but I do still think the extra work required to do so would deter some, if not most of the bad offenders. I've been wrong before though.
Thanks for the reply!