Siege events is not about to open an tower. You would never win these events when you raid with your main army. In this case you dont be behind other races.
When you open an tower - normaly its not full of gold. In honor events you can clear the first two waves with bronze and go then with your main army. Until this events, enemy also siege and/or having enough to do to route other people.
To open tower - loan 4 rockets (and make sure you get an good nora and grimms before). With 5 gold Scorps, 4 rockets, one spider (or mummie) and 7 heros you are able to do serious siege. You do way better then dwarfens with silver mechs, scorps have an double heal (vega and themself).
Sure - you have to put your goldcap into Scorps, you would loose sometimes a Scorp and you have to priority Scorps and Siege research over Spiders.
But - Only because Lich is no meta faceroll afk race like humans in siege - dont tell me it isnt possible.
The best players are that who love their race and dont care about playing meta.
Every Race can siege as long as we have the loaning mechanic. I saw wonderfull attacks as Rakan, with full gold monks front and loaned Archers. He loose about 1-3 monks per siege (and they cost only bloods)
So i recommend - play what makes fun and them look how you can negativ the downsides. I like Lich and dwarfens, as Lich you can push you goldcap into spiders and whaiting all day they someone accept duells, or you go an other way and have fun farming ressources
And i forgot as the post above me - he is right.
Dwarfens loot the best, and have bonus on timers - downside for the good incommings is theirs cost inefficient (garrison and main army)
Humans are the best overall class, not the best looters, not the fastest class and not the best garrison, but also beeing not behind in any single situation.
Lich are very cost efficient and their downside is the incoming (siege and timers).