Which is why I laugh every time people in this and other threads go on about ground-pounder marine lists being as good or better than the standard marine list. Ah Ah Ah!

To respond to a few bits:
(snip)

One of the goals of rebalancing a list is obviously to tweak under-performing and under-used units. I’m bemused that you're even questioning this or ranting against it happening. Rebalancing such units encourages more variety of competitively viable lists, which can make the army more interesting to play with and against. It's also better for players owning those models to have a good opportunity to use them rather than them being rarely/not used.

It is a significant failure of the list that those options are relied on. The SM and Adeptus Mechanicus Titan Legions are separate organisations, both fiercely independent and with their own interests. Titans are also rare and not commonly available for SM battles whether the SM would like them to be or not. Sometimes Space Marines may be lucky to have Titan support for a particular battle, but often times there won’t be Titans within thousands of light years of the planet they are fighting on. No one is suggesting removing allies from the list, but they shouldn’t be such ‘must have’ choices and the list should be able to function nearly as well without them. The potential points cost raise to 300 in addition to the worse critical could help matters a bit and I do have a left field suggestion that could help the list rely less on allies, but I'll write and post that up another day as I've spent a lot of time here again today when I have loads to get done.

I contend that Vindicator cannot easily be made 'competitive' through cost changes alone, purely because by design it has a very niche role; other formations give the player more options and better results. IMHO, to make the Vindi more desirable you would have to change the unit stats to the point where it would no longer represent the "Space Marine" Vindicator, which defeats the purpose of the exercise

To some extent this is the reverse of the Vindicators question. The Marine list is undoubtably harder to use without titan capabilities, especially with the "power-creep" that has been the hallmark of many later lists. But increasing the cost of individual Warhounds to 300 points will not necessarily stop people from using them, it will just shrink the points available for real marine formations, reducing the list capability and thereby weakening the SMs list as a whole.

Then the list needs some appropriate other way to provide what the Warhounds do

To me what this indicates is a need for an additional source of ranged Macroweapon, or some access to Titankiller weaponry

the Vindicator, which I cannot remember ever being used either as an upgrade or a formation in its own right – but I would equally have to ask, “so what”?