Lancer is great. It is complicated, not as complicated as battletech though. Which to me is great for getting new players in.
The best way I’ve found to teach people in that system is to create a new character in their character sheet/compendium website, comp/con. And then have a GM to run the game and help with concepts. License Level 0 (starting level) is very restrained. The next level (LL1) opens up interesting opportunities. And then LL 2 is where your options become a bit opportunity heavy.
The official discord is active and there are several other side discords that are active. I’m currently both playing and GMing. There is a reprint of their physical book coming out next year.
As for the lore, there are 4 manufacturers. The post office, anime, luxury cars, and cthulhu mechs.
With the online tools it’s free for players, GM pays for background information and npc stats. There are foundry and roll 20 that can run this for online play.
Combat is fundamentally an easy concept. D20 to see if you hit and D6’s for damage. Although if you have 5 players you can easily spend a session on just one combat, which from what you said is a downside.
I don’t think I’ve stopped in the middle of something without planning on coming back. If something is difficult I’m more likely to do better the next day.
But something that I know I would not have fun with is platinum any Yakuza game. And honestly, I’m glad this game taught me to not worry about not completing things I don’t care about.