It seems pretty unanimous about the 13 seat loss, from exit polls to democratic strategist, to political pundits and the Democratic panel who did their after action reports. Even democratic leadership admit it.
As for what you raised about the GOP, I think you seen the results in how independents voted. They left the GOP, not voting for GOP candidates in 2018 and not voting for Trump in 2020.
Somehow though, there were a lot of these folks who voted Biden, against Trump and then GOP down ballot. How does a group of voters vote 54-41 for Biden, yet vote only 50-48 for Democratic congressional candidates? There has to be a reason or reasons.
It's possible what you stated stuck to Trump and when it came to congressional candidates, doing away with the police over rode that. At least in those 13 races. But not all others. For something to stick, it has to be plausible. Tagging Trump as a racist worked among independents, tagging democratic congressional candidates as wanting to do away with the police, defund the police worked on some. Where it wasn't plausible, it didn't work.
But what left pundits and political strategist scratching their heads is how can Biden win an election by 7 plus votes and yet lose house seats. This was the first time something like that happened since 1884. 1884 was the only other time. Something was at work to cause that. The dislike for Trump was hot and heavy by independents. But not so much for Republicans congressional candidates. The dislike of Trump didn't reach that far down. But something had to cause that, the not reach.
The best any of us, those who forecast and ended up with egg on their face when the democrats lost house seats is Defund the police. That became the number issue in many voters mind when it came to their vote for congress. But not for president.
I suppose we all are still trying to figure out the reason why. Defund the police is a consensus reason from both sides of the aisle. But it could be the dislike of Trump which drove folks to the polls just didn't register down ballot.
It could be the districts themselves. National polls, they don't mean much when the election is district by district.
One other thing here. I'm not trying to help Republicans win elections. If I was I would be giving my advice to them and not to Democrats. I'd be telling Republicans what to change, what not to say, how to attract the independent voter, not telling democrats that.
But that's okay, the base of any party doesn't want to hear why they lost.