Contrary to popular belief, original Homeworld absolutely
contained (link pointing to documentation of original HW source code, check "AI Scripting System Specs.doc") enemy fleet scaling. If it didn't, it would become ridiculously easy extremely fast - essentially you'd just select all you have, attack order the enemy and wait for the results. Remastered version changes scaling in order to accommodate balancing changes, but difficulty-wise, it remains about the same - enemy fleets are designed in order to give you a challenge regardless of your fleet size, however your fleet size helps you by giving you more options in overcoming the enemy, effectively making the game easier anyway (so it's not like building a large fleet is pointless - besides, epic space battles!)
So basically... If you want the game to not be a challenge at all, disabling scaling will make it so since the way scaling works is by adding more ships to "player arrives with next to no fleet" baseline. If you wish to play it like it was intended, leave the scaling in.