Now you're not really making much sense. So Steel Fists are somehow decent fast counters while Hikers aren't? They have the same movement and the same attack range, yet Hikers are worse despite having better stats? Is the implication here that Force Field is worse than Reactive Armor 4? If that's the case, then why are Wardens apparently able to survive so well and Hikers aren't? Wouldn't their battle against Sentinels also end with the first turn having '2 dead and 1 critically injured'? It's the exact same first turn in battle with the same unit lineups, just units from two different ages. Each turn beyond the first is essentially going to be a repeat of itself until one side is defeated, and fast units don't have the attack range themselves to really spread out in such a way that the heavies can't still gang up on them, not that it should take more than 2 heavies to bring down a fast unit anyway. If it does, it's probably a % boost issue more than the units being used.
Tbh I'm pretty sure your experiences are different from others. I've seen enough battles in which hikers can't survive better than steel wardens or steel fists. Perhaps keen eye plays a role, perhaps reactive armour better counters keen eye's effects, perhaps something else. Another thing I've observed is steel wardens' capability to never being unable to hit a certain sentinel. With steel fists and hikers I have. This are just my observations. Also in OF I've seen often enough times where even eels striking in their 1st turn, some crabs can't attack them. Despite better range than the mentioned space heavy units.
In my observations: often shredders, steel fists and hikers can't attack some fast units in their 1st turn. If you could provide evidence that disproves that the outer left/right positioned shredder, steel fist and/or hiker can hit every fast unit in their 1st turn, it would be of great value to prove and verify your claim: range doesn't matter, heavies can hit every fast unit in their 1st turn.
What's however is important to Titan, is that the heavies can't survive well enough. Perhaps the devs have given it stealth on rare terrain to compensate for this. However it doesn't help units that cant survive the 1st fast attack wave. Which is imo the biggest issue in regards of balance. As it effectively making the Titan's heavy a paper tiger. Which is just silly for what heavies' role in balance could've been.
From my personal experiences, with abyssal gliders vs Titan units. The abyssal gliders find it particularly though to kill the light units. While they didn't struggle as much with hikers and need only 1-2 attacks to defeat heavy Titan units. So, light might be ironically the best bet against fast in Titan. At least with own age only restrictions. If one wants to use AO support vs fast units. Though I would still rather opt for fast vs fast combat, depending on what's in the 2nd wave of the common 2-wave battles. So, maybe light/fast counter fast, art. counters everything except fast/little bit range, range units counter decently art, light perhaps, heavies and other ranged. Though I still rather opt for SAJM ranged due to the better contact! Ability, unless I'd like more fire power which blast offers.