Income tax is only paid by people who have no choice but to trade their labour in return for money, i.e. the working and most of the middle class. The very rich get their income from return on capital (e.g. being a landlord) and if you own your own business, you can do things like paying yourself minimum wage and having your company provide lots of the nice things in your life. All in all, what this means is that income tax alone is fundamentally incapable of causing proper redistributive change. If you whack up the income tax for the highest earners, you encourage them to switch to other forms of income that the tax doesn't cover. If people in Scotland did this, not only would the Scottish Parliament lose the tax revenue that the person managed to avoid paying, but they would lose all of the tax revenue of that individual as the revenues of the taxes they now pay are not devolved. This isn't a political point where one party is right and the other is wrong, this is a statement of fact.
Devolving income tax is a politically devious scheme because most to most voters, income tax is the important tax that actually matters. In the real world there are a whole series of other taxes which can have as much, if not more, of an effect upon redistribution and their own wellbeing. The OECD has actually said that developed countries should start shifting the burden of taxation away from taxes on labour because they are pretty inefficient and cannot ever be fully redistributive. In any case, we're not going to have a lot of choice in the matter because automation is going to wipe out most of the the income tax receipts as significant proportions of the population become unemployable and the rest have a race to the bottom of pay and conditions for what work remains. This is actually already happening with the zero-hours contract and gig economy, and is one of the reasons why we absolutely have to plan a move away from income tax.
Council tax is a property tax and is one of the sorts of taxes which the OECD says that we should start to focus on. One of the main reasons for this is that rich people don't tend to buy worse properties than they can afford just to avoid paying tax. There's no downside to finding a way to avoid or reduce their income tax payments but the downside to not living in the posh bits of Scotland is that, well, they won't be living in the posh bits of Scotland. Evasion is therefore much more limited, so it's actually possible to increase the bands at the top end and actually get that revenue. There's still a way to go though, as the system is still not progressive enough.
The ScotRail franchise is probably as close to being a concession as was possible under the law at the time. The concession model would be a useful halfway house between a private and a public sector operation, since you can avoid the idea of the private company getting the ticket revenues even if its performance is poor. It also avoids the problem of public sector companies where efficiency savings are stopped for political reasons, even if they would have a net benefit to the country as a whole.
