Razvan - Good points, mate! I did actually say that the kit 50-200mm is regarded as "very ordinary" - which means, usable, but not very good.
If you check the ratings on Pentax forum - "both" of the 55-300s are rated as best-quality for price "consumer" lenses. Not as good as the Pentax "*" grade lenses. The "kit" L 55-300mm is "lower" grade because of the lack of quick-change and the plastic mount, compared with the ED DA version.
The usual comparison is with Sigma's 70-300mm DG APO, and it rates better than that.
There IS actually a "reason" that I "sound fanboy" about the 55-300.... Where I am - Australia - we don't get the L 55-300mm as a kit-lens at all... The closest we get to "any" x-300mm in a kit - is Sigma's non-APO 70-300mm, which isn't really worth shelf-space. The L 55-300 as kit lens seems to be limited to North America - and I did hear of an EU deal, but the mention was because that was rare, there.
If we want a Pentax 55-300mm here - it's the DA ED version - which costs $670.00 - a lot more than in the US. If I get around to buying one - it'll be an "as new" offer on Pentax forum - a recent such offer was at $325.00 - less than half the amount we pay here.
And sure - you are indeed correct - the Pentax 55-300mm is a good consumer lens, but not exceptional optics. Why did you think I also mention the K-mount and Takumar primes? The K-mount "M" series 300mm prime sells for around $300.00 - the Takumar 300mm prime for a lot less.
As you'd know - either is far better optics than the 55-300s... For very much less than we pay for the DA ED here. I'm a a hobbyist. I use a tripod often. A semi-manual or manual 300mm prime is therefore no hassle...
As for the Pentax 17-70 f/4 - sure, a very good lens. A friend in Denver has one and swears by it. Denver is in the USA, so that lens is at US prices there. In Sydney that lens is $725.00. And, at least here, certainly isn't offered as a kit deal.
What IS offered in that size, as a kit option, is the Sigma 17-70mm f/2.8-4.5 Macro, Retail, $339.00 in Sydney - but about $220.00 as a kit deal. Okay - of course it isn't as good as the Pentax 17-70 - but it IS better as a walkaround lens than the kit 18-55mm (I actually already have one of those - $45.00, as new, Gumtree auctions) - as it has a bit more reach, and starts at f/2.8, not the 18-55's f/3.5.
Must agree - the Pentax 17-70mm is "a great lens for the money" - but some of us have to work within a firm budget - and $725.00 for "one lens amongst many" in one's collection, doesn't fit such budgets too easily.
Better - at hobby/enthusiast on a budget level - to have the kit 18-55mm, and the Sigma 17-70mm as the walk-arounds - and go to the K-mounts and M42s for the "good optics" primes - that do still fit the budget.
And, I'm not having a lend of you, mate - if I won a nice big lottery - you'd be run-over in my rush to buy a beautiful D700 - and a truckload of the superb lenses and gear to go with it... (A D700 with Nikkor 24-70 AF-s f2.8 G Lens - is $4,455.00 here...)
But, things being as they are, the K-R is by far the best value for limited money, around - that, and all the FSLR lenses....
Sometimes - being "on a budget" - can be somewhat peeving....