Russia vs Ukraine in a void, sure, Russia has more resources (though they haven't used them to build up and modernize their army enough - and what good is ore in the ground if you cant' process it fast enough?), more manpower (but their morale is far lower and their training is, as well).
If one takes stock of the areas where it is easiest to establish relative strength in conventional warfare, then Russia is superior in manpower (as you mentioned), in the size of their defence budget, and in their possession of a formidable full-spectrum arms industry.
In terms of equipment numbers, the pre-war relative situation was overwhelmingly in favor of the Russians in all categories. The extent of that in the current situation is more difficult to establish, since both sides of the conflict seem to be in the habit of extensively misreporting their own losses, and those suffered by the enemy. But even if we take the Ukrainian numbers as accurate, Russia should still have disheartening amounts left, even with the supplies by third countries into the Ukraine. There have been reports of Russia facing equipment shortages, though it is much more difficult to determine if these mean absolute shortages (the stuff does not exist), or if it a question of logistics (the stuff exists, but is not where you need it to be).
Ukraine no doubt enjoys an advantage in morale, which seems to be an area the Russians are struggling with. There are also reports of Ukraine enjoying an advantage in military leadership, made all the more potent by the Russian failure to appoint a single individual as theater commander until April, violating the principle of unity of command. Ukraine also seems to have better intelligence, in large part provided by third-ciuntry assets, whereas tactical recon is not the Russians' strong point.
Third-country aid in military materiel certainly needs to be taken into account. Particularly the provision of HIMARS systems to the Ukraine in June appears to have made an impact. After the initial Russian parade ground invasion got a bloody nose, the Russians fell back to their usual tactic of massed artillery, with good reason: it works. The period saw the greatest gains in ground by the Russians during the invasion. But HIMARS began to make a difference by targeting the Russian supply depots, causing periodic shell shortages to Russian artillery.
Without international support and backing, Ukraine would fall. I don't think anyone really disputes that. There'd be a guerrilla movement and unrest for years to come, but Russia could probably take Kyiv simply by brute force.
And that is the problem as I see it.
According to Finnish military open sources, Russia appears to be settling in for a long war. According to their assessment, Russian reinforcements from last month's partial mobilisation haven't yet reached Ukraine, and that it would be advantageous for the current Ukrainian offensive to be maintained as long as possible (edit: other sources estimate perhaps until late October before the offensive begins to lose steam) in order to regain as much lost ground and defensible positions as can be before they do.
Link, only in Finnish I'm afraid.
If they are correct about Russian intentions and preparation for a long war, then the Ukrainian ability to resist Russia in the long run is dependent on the continued willingness of third countries to keep supplying them with advanced (and expensive) military hardware, in sufficient quantities, for the foreseeable future. Now, nobody knows about the future, but it seems to me that this is not necessarily a given, in a world of elections, budget cuts, and policy changes. How far is the natural sympathy felt by much of the world going to carry things?
To be sure, my personal sympathies and hopes rest with the Ukrainians. Their best chance, as I see it, is for military materiel support to keep on coming from the outside, with ever stricter sanctions targeting, among other things, component supply chains to the Russian arms industry. I'm just not at all sure if we collectively have what it takes to keep doing what needs to be done in order to make things work.