True, though history seems to show that copy only happens after they aren't able to buy or invest. It's much riskier from a business perspective to copy than to buy usually.
Only for really big things like Instagram that have a network effect helping them, and as such threaten the incumbent.
For smaller features / ideas, it's much less risky to copy than to buy a company (for, say, 10-100M) and hope the acquisition goes well. Most acquisitions don't go all that well.