Collectivity, as interpreted to mean flow of a dense medium in high-energy nucleus-nucleus (A-A) collisions and described by hydrodynamics, has recently been attributed also to smaller collision systems -- p-A and even p-p collisions -- based on certain analysis of LHC data. However, alternative analysis methods reveal that some data features attributed to flows are actually manifestations of minimum-bias (MB) jets (dominated by jets near 3 GeV). In this presentation I describe the differential structure of single-particle hadron $p_t$ spectra from SPS to LHC energies in the context of a two-component (soft + hard) model (TCM) of hadron production. I relate the spectrum hard component to measured properties of isolated jets. I use the spectrum TCM to predict the systematics of ensemble-mean $\bar p_t$ in p-p, p-A and A-A collision systems over a large energy interval, with accuracy at the percent level. Detailed comparisons of the TCM with both spectrum and correlation data strongly suggest that MB jets (jets being also a "collective" phenomenon) play a dominant role in hadron production near midrapidity. Claimed evidence for flow phenomena is better explained (more simply and quantitatively) as jet manifestations predicted via measured properties of isolated jets.

Collectivity in high energy collisions