Don't get me wrong, but burn rate charts can be very misleading. As often as not, a propellant that "fills the gap" already exists due to other historical needs that put it in the catalogs. It is very easy to invent a new case volume and bullet weight design, but not as fast to produce new propellants
Burn rate charts are indeed very misleading for Viht powders and there are very few (if any) true 'gaps'.
VV seems to have no interesting the single base line vs proliferating all kinds of new N500 series powders.
I suggest you go to the trouble of accessing the relevant data for the N100 series powders and also N555. As a shooting friend pithily described N555 when it was introduced: 'the N100 grade that pretends it's a 500!'
Being designated as an N500 series grade, it presumably contains some nitroglycerine, but it has to be very little on the evidence of its nominal specific density and energy values, where on both counts it has little in common with older N500 grades and is right in with the N100s. In fact two N100 grades have higher energy values. Burn speed wise it is just a hair 'quicker' than N160 as seen in max loads for most applications, but is better suited to medium capacity 6.5s.
I'd dispute there is a large gap between N160 and N165. Look at the list of actual applications in Viht's loads tables (shown at the end of each grade's description on the website) and then at actual loads / MVs in some of those tables. I'd assert that the gap between the pair is no larger than those in other companies' grades such as IMR4831 to 7828 and Hodgdon H4831 to H1000. I happily use N165 in a 243 based wildcat, 6.5X55, and 284 Win with 175/180s all at normal match level MVs. Other people I know prefer N160 in these applications obtaining similar MVs, certainly no higher. Again, these powder tend to be 'quicker' in real life applications than burn rate charts show. N160 is not slower than IMR-4831 and next to the H version as many charts show - in practice it falls between the 4350s and 4831 and in many applications is closer to the former.
If you take a quite different type of chart, that used by Norma, and based on actual pressures generated in 308 Winchester with a fixed powder charge weight
https://www.blaserbuds.com/forum/viewtopic.php?t=14866
you get a completely different set of results. N160 is shown as 'quicker' than the benchmark IMR-4350 whose pressure is indexed at 100, the Viht grade producing 107.5.
How many grades do you expect / want? Excluding N110 which although nominally a 'rifle powder' is really a magnum handgun grade, and excluding 50 BMG propellants, there are 16 rifle grades. The handloading market in isolation cannot support any grade without other markets - there have to be wider bulk powder markets for commercial and military cartridge applications. Recent Viht N500 product introductions that you complain about are geared to wider user demands whose sales volumes will outstrip those from leisure shooters. Fairly new N565 for instance is primarily geared to .338 Lapua Magnum military applications, and we get it as a benefit on the side.
If you don't like the idea of the N500s and nitroglycerine, well then, stick to Hodgdon's ADI manufactured single-based products of which there are nine from H322 to Retumbo, same as Viht from N120 to 170 (arguably 10 in practice given N555's low energy levels). Almost every powder introduced by any propellants company in recent years contains nitroglycerine, including IMR breaking tradition with the five -ill-fated Enduron grades, all of which were double-based.
