Except in rather special circumstances, I would not expect any short term Treasuries to be as good as a diversified equity ETF. I say this mainly because of the 7% or so historical return from equities, compared to even longer term bonds of only 3.5%.[ https://www.joshuakennon.com/stocks-vs-bonds-vs-gold-returns-for-the-past-200-years/ ]
Of course, anybody who has fixed, short-term obligations which they know the cash value of and can only meet by preserving almost all of their capital will not want to risk an equity bear market. Treasuries, especially short term treasuries, such as the 1-3 year bonds you mention, and which have a known cash return, extremely low volatility and are generally assumed to be riskless, could then be ideal.
Long-term investors should expect to be better off with the higher expected compounding annual return after taking account of volatility. The Kelly criteria
[ https://www.stat.berkeley.edu/~aldous/157_2016/Slides/lecture_2.pdf ]
will tell you how much better off, and will even tell you the optimum proportion of your capital to invest in volatile equities, rather than safer treasuries. Except when P/Es are astronomically high so expected returns are exceptionally low, the numbers seems to me to recommend a 100% investment in equities.
The same formula, and recommendation even applies in the short term, provided the type of obligations above do not apply and the investor has a utility function which is logarithmic.
[ https://www.economicshelp.org/blog/glossary/expected-utility-theory/ ]
Given the suitability of equities for both of the above, the main groups for whom Treasuries are suitable would seem to be banks, pensions funds, and other people looking after other people's money, and for which it would be unforgivable to loose money.
Since financial advisers, also come into this category, I should say that I am not such an adviser, the above is not advice, and equities can loose money. In fact, it this risk and the fact that it cannot be diversified away that gives the expectation of reward. I should also declare an interest in the above as someone who is fully invested in equities.