When we say a character has good footsies it can be about these aspects:
- Good reach
- Good movement
- Speed of said moves that have reach
- The long range normals being mid
- staggers and recovery (although this is also relevant for rushdown)
- moves lead to hit confirmable combostarters
- Pushback on block
Take Jax for instance. He has a 9frame mid in f3. However, its range is very poor and f3 and f33 itself have a lot of recovery, thus whiffing this move is super easily punished. F2 is better in terms of footsies as its reaches further, is safe and has good recovery making it harder to be whiff punished - but it's a bit slower. Jax archetype is rushdown character - he wants to be in your face where the reach of his normals dont matter as much. Jax struggles against Kabal and Cassie due to them fundamentally by design having better tools of playing footsies with.
Going back to the Johnny example - lets put Cassie in the opponents place instead of Kotal. Cassie has access to an 11 frame mid in b2 that has almost the exact range as f3/f4. F2 is 10 or 11 frames and goes just as far as f3 - it's just much faster. Already now you should see why Cassie excels at this playstyle by design.
Johnny has good footsies but lacks a particularly scary stagger game as his moves either whiff (lul) or the moves simply being too slow. F3 being a high also makes poking out of staggers so much easier. The move also doesnt add pushback, this if I f3 and it gets blocked and I try to shimmy I can get blown up due to me being negative on top of being in her face and not blocking as I move backwards - point is, Johnny has to condition you to make use of his strong footsie toolset as he is not a particularly scary rushdown character lacking mid, hitconfirmable strings to punish opponents disrespecting frames with low profiling moves, thus requiring him to
set up shimmies himself as he does not have the pleasure of having ressource free shimmy setups due to pushback (Think Scorpions d4 and f34 on block)
Going back to the list of footsie aspects - Cassie can put a big fat check at almost all categories for her mids, with f4 only lacking some reach, but this is where f2 and b2 still put the rest of the cast in the dust. F2 leads to a Krushing Blow on a whiff punish and otherwise
plusframes on block. She's probably the only character with a gapless string that ends with a plus on block mid. F4 has pushback on block while leaving her neutral on block. It's also a hit confirmable mid if it connects. Due to it being 0 and automatically putting space between the opponent and herself she is already in an excellent position to apply shimmy. She's safe from retaliation at this point and the opponent fear her other advancing long normals. Cassie by design have a
much easier time applying shimmies and force whiff punishes compared to other footsie characters due to her moves doing a lot of the setups for her. You can see Cassies literally standing still waiting for pokes to miss and then they just whiff punish with f4.
Thus, the player will have to make decisions, but the decisions in Cassie's case are no brainers often resulting in strike/throw mixups and there's little movement involved (and even lesser risk involved) with her footsie gameplan thanks to her amazing tools.
Sorry for the long explanation my man