If you turn on reflective TK'ing in TDM and Siege, a whole lot of people who don't know how to play are going to be upset, because they'd be killing themselves on their teammates. Personally, I think this would be better for the game though. Just like in Warband, have reflective damage on so when you hit a teammate, you take damage. This would force people to not swing weapons like derp heads and actually focus on landing their shots. Siege battles were definitely more fun as well. You'd have people actually using shields to approach a wall, rather than an army of 2hrs swinging around like a giant mobile meat grinder with zero threat to harming themselves.
As for skirmish, the way I see it, the game mode is clearly modeled after the style of comp play that went on in Warband, which was 8v8 or 9v9, 1 life, flags spawn at 10 minutes. My only gripe with skirmish mode in BL is that we are 6v6, and the maps are kind of small. I'm not really a fan of having an archer being able to post up and shoot at any flag they want, because the maps are small. If the size of the maps were 1 1/2 times larger, I think it would be perfect for 9v9 play. You'd have more space in between flags, which would mean that you'd have to be a bit more tactical on where you choose to hold. Roaming cav would be a bit more important as well, and there would be higher risk of them going off on their own as their team would need just a bit more time to reach them.
Battle mode needs to come back. 20v20 TDM, 1 life, large-ish maps, a flag spawns to be capped after 10 or so minutes. It was by far the most popular game mode in Warband, and would be amazing in BL. TDM definitely is popular at the moment, but to be honest, I think that is because it is on a server list rather than a queue. You do not need to wait to get into a game. But this all goes into bringing in player run servers or just server listed servers.
As for the OP's argument of waiting around to get rekt'd by experienced players. Yes, well... that is going to happen in any game that has a niche community that adores the game. Have you tried playing Gears of War 3 lately? You will get destroyed if you don't spend hours learning how to git gud. Until we have a larger player base, that is just going to be the case with Bannerlord too. People who have 2k+ hours in warband are absolutely going to slosh a few newbies who've only played BL and are coming from singleplayer. Not much you can do to change that.
-- I also think that spawn points should be a thing in TDM. With the way the gold system works, it can be annoying to play the class you want to play when you keep spawning into the enemy.