1) Since you already have a mix of many funds, including individual index funds that target specific asset subclasses, if you do want to do "tactical asset allocation," tuning the proportions of stocks and bonds in your portfolio in response to market conditions, that might mean that you are a sophisticated enough investor that you would be better off taking the direct reins and going entirely to using separate mutual funds for stocks and bonds rather than adjusting the mix between Wellesley and Wellington.
Your holdings seem like a sort of mish-mash of overlapping offering to me--don't let that sting, mine were the same way for a long time and I don't think it did me any particular harm, but it doesn't lead to clear thinking. I don't think it makes sense to have more than one all-purpose balanced fund-of-funds offerings--in your case, Wellesley, Wellington, and LifeStrategy.
Even if the only two funds you held were Wellesley and Wellington, a large change in their relative proportions would make only a small change on your stocks/bonds allocation. If you actually believe in and care about their active management... you might say "I want more violins so I'll mix in more Philadelphia Orchestra and less New York Philharmonic," but you also get a different conductor.
2) You say "prevailing wisdom seems to be that bonds will underperform stocks over both the short & longer term." Well, that has always been the prevailing wisdom. Stocks are supposed to outperform bonds. That's what the risk premium is about. So why does anyone hold bonds at all? That's what the risk premium is all about, you can't get the risk premium without really taking the risk. You have to stop asking what you predict for the price movements of bonds, and ask why you have them in the first place. The prevailing wisdom is also that bonds have less risk than stocks over both the short and longer term.
3) Probably always, but certainly now, attempts to hash out what direction to dodge in are ill-advised. We always get a mass of conflicting signals, and the danger is that one will choose a direction based on emotional considerations, and then filter the information to see only the signals that happen to point the way we feel like going anyway. Ignoring enthusiasts and promoters, the consensus long-term view from people who seem to be knowledgeable is that stocks and bonds are both in for a long spell of lower-than-historical returns. Well, stuff happens. Better to accept that than to listen to promoters of weird stuff we'd never have considered normally.
4) Tactical asset allocation was all the range 15-20 years ago, and there were numerous tactical asset allocation funds that offered to do it for you. Investment ideas never go away, but these funds as a class pretty well systematically underperformed those that just held steady, and you don't hear much about them any more. One of Larry Swedroe's books has some absolutely devastating statistics about them. You'll notice that although they actively manage the stocks and bonds in the portfolio, neither Well[b]esley nor Wellington tries to do tactical asset allocation[/b]. If they don't think it's a good idea, why are you trying to do it for them? Vanguard used to have a tactical asset allocation fund, which they used as a component of their LifeStrategy funds. That fund has been terminated and the LifeStrategy funds now have unchanging, locked-down stock/bond allocations.
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness; Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.