The Wall Stats vs. The Tower; I'm missing something

Recently unlocked the wall and have 4 labs running:

Wall Thorns (1% per level) Wall Regen (10% per level) Wall Health (2% per level) Wall Fortification (20% per level)

Advice I was previously given was to get Thorns and Regen to level 10 (so, 10% and 100% respectively) and Health to 25 (so 50%). The community was torn about Fortification in general, but it's not busting my bank so I can take to to level 10 (200%).

Here's where I'm confused. Why is The Wall any better than my tower? It looks like it will significantly underperform.

Thorns: Just 10% of my Tower's 99% is only 9.9%. That's a lot of hits to take anything down.

Regen: 100% of my tower base is the same as my tower base, right? No improvement there.

Health: Even 400% (200% base +200% from Fortification) is less than the 1650% 16.50x max recovery stat I can currently pull.

It appears on paper that every stat is the same or better for my tower than it is for my Wall. So the wall will always fall before my tower ever would and effectively leave my Tower to face the same enemies as usual without any extra support. I realize this isn't how it actually happens. I watch a boss just hover on The Wall for 20 seconds with the wall taking no damage. So I know I'm missing something important...

What am I missing?