One of the key elements of list building and strategy in Star Wars: Legion is the balance of quality and quantity.
Many people have posited that the more activations you have in a list the more of a competitive edge you have over your opponent, while others assert that some of the more expensive units are untouchable by small unit spam and that they have the competitive edge; and the fact is that neither is right - but neither is wrong either despite these two philosophies being at odds with each other. There is a spectrum and balancing game to the quantity vs quality of Legion list building; and understanding the strengths and weaknesses of each aspect as well as your personal play style is what is required for the true list building advantage.
There is a strong argument to be made in the case of activation spam. More activations after all means that you have an advantage in deployment, being able to deploy less significant units first and then able to counter deploy key units against the opponents key units giving you a favorable matchups between units during the game. Similarly more activations gives you an advantage during the game allowing you to postpone your valuable units until the opponents activations are spent, allowing you to activate those units with impunity. More activations also gives you an advantage in certain scenarios that count number of units towards win conditions, such as Intercept, Breakthrough, and Key Positions.
Expensive elite units also have a strong argument for the competitive advantage they bring. Elite units often throw around enough fire power to end small units in a single attack, while also being durable enough to survive several rounds of attacks from small units (if the small units can even scratch their defenses at all). Elite units also tend to have keywords and abilities that specialize them and make them excel in situations. An advantage that can’t be made up for with a difference in sheer volume or numbers, which gives them another area that they can out compete generic units in giving them the edge.
They both have their drawback though…
Unit spam might have the upper hand in activations, but against elite units that can sometimes mean very little. Small units are eliminated relatively quickly and easily compared to their more expensive counterparts - likewise they tend to throw few dice themselves, meaning that they often can’t overcome the constants in the game such as Heavy Cover and dodge. Activation spam also has to stretch itself across multiple unit types to get a high enough number of units, meaning that often activation spam can’t completely control its order of activations and can often trip over itself when it finds that its command cards don’t cover everything it needs.
Elite units are expensive so you get fewer and can have trouble projecting control over enough area of the board, giving the opponent control over where engagements happen and control of the objective in certain scenarios. Elite units also can put out a large amount of damage, but only to one unit at a time meaning that often you will be overkilling small units and wasting work - or allowing several other units to go unchecked.
Assuming that your intention is not to skew all the way into one aspect or the other, the obvious solution is to balance the two. A well balanced army will often have an element of elite units who are hard to deal with and specialized in situations as well as a sizeable amount of spammable units to cover the weaknesses of the elite units as well as to offset the opponents activation count or push the advantage of their low activations… bringing balance to the list.
One of the hardest things to do is know when a list is balanced on this spectrum, as it will be different for every players style as well as change for each opponent they face - so here are some general guidelines and starting points.
General Guidelines for Building a Balanced List
Activation Count: between 7 and 10
340~ points of spam units (5 rebel troopers with Z-6, 5 Stormtroopers with DLT, etc.)
340~ points of elite units (Weiss ATST and Veers, Veers and three bikes, Han with Leia and Chewie, etc.)
120~ points of flex to shape more towards your playstyle and army strengths (keep in mind rebels will tend to skew quantity and imperials will tend to skew quality, but that isn’t a hard and fast rule).
every unit should either throw enough dice or have enough keyword abilities to deal 1 damage on average with every attack against units in heavy cover or with Armor.
The two aspects of your list (quality and quantity) should ideally support each other in some way
Again these are just general guidelines and suggestions to help you build and check your list before you play a game. If you play the list several times and it is not performing as you envisioned, make a change.