Yes, there is less American military hardware in Europe now. But Russia is also still further away from the places that the U.S. and NATO guarantee via Article V of the NATO treaty than in the old cold war days. And Russia's military is not the same as the old USSR's.
Most importantly, the US, France, and the UK still have nuclear weapons, which are and always have been the key to deterrence in Europe. Indeed, for most of the cold war, these nukes offset Soviet supremacy. These days, is Russia militarily supreme in Europe? I am not so sure. The Russian military has been far from impressive since ... mid-Afghanistan. Whereas the US has demonstrated superior skill on a conventional battlefield. So, unless Russia tries to launch an insurgency, I think we are ok.
The reality is this is not about hardware but about interests:
“The American people are not going to war with Russia over Ukraine, full stop,” a senior administration official said, echoing public comments by Mr. Obama.It really is that simple. The asymmetry of interests in Ukraine make it abundantly clear that we cannot deter Russia now. It is not about what we have but what we are willing to use. This asymmetry attenuates the further one moves from East to West. Given the World Wars and the Cold War, Poland now is guaranteed via NATO its security. The Baltics are a smidge harder to assure, but NATO has repeatedly acted to protect the reputation of the alliance. That really is what motivated the Bosnia moves in 1995, kept NATO together despite differences of its members during the Kosovo campaign, and kept everyone in Afghanistan far longer than one could otherwise reasonably expect.
The pattern is consistent--when NATO as an institution is under threat, the members do what they have to do. A threat to the Baltics or to Poland would raise questions about NATO itself--and that is the tripwire.
So, before we worry that the US and its allies are only spending two or three or six times as much as Russia, we need to look at the alliances, the commitments, and who is in and out. By the way, whose power is added to Russia's as it contemplates any potential aggression? Oh, none. That's right--Russia has only weak supporters and no allies in this.