True.  Part of the issue rests on the block sync horizon/cliff.  There is a value X which is the average number of blocks the 90th percentile of nodes need in order to sync.  It is sufficient for the [semi-]pruned nodes to keep X blocks, after which nodes must fall back to archive nodes for older data.

There is simply far, far more demand for recent blocks, and the demand for old blocks very rapidly falls off.

There was even a more radical suggestion years ago - refuse to sync if too old (>2 weeks?), and force the user to download ancient data via torrent.

On Tue, May 12, 2015 at 1:02 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:

On Tue, May 12, 2015 at 7:38 PM, Jeff Garzik <jgarzik@bitpay.com> wrote:
> One general problem is that security is weakened when an attacker can DoS a
> small part of the chain by DoS'ing a small number of nodes - yet the impact
> is a network-wide DoS because nobody can complete a sync.

It might be more interesting to think of that attack as a bandwidth
exhaustion DOS attack on the archive nodes... if you can't get a copy
without them, thats where you'll go.

So the question arises: does the option make some nodes that would
have been archive not be? Probably some-- but would it do so much that
it would offset the gain of additional copies of the data when those
attacks are not going no. I suspect not.

It's also useful to give people incremental ways to participate even
when they can't swollow the whole pill; or choose to provide the
resource thats cheap for them to provide.  In particular, if there is
only two kinds of full nodes-- archive and pruned; then the archive
nodes take both a huge disk and bandwidth cost; where as if there are
fractional then archives take low(er) bandwidth unless the fractionals
get DOS attacked.

--

Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/