In the vast majority of games, the life that your opponent gains from you nuking their creatures with Swords to Plowshares will not amount to much, unless theyre playing a black deck with life-to-resource cards (watch out for Toxic Deluge or worse, Yawgmoths Bargain !) Swords to Plowshares isnt a particularly expensive card, and its very easy to find
As for closing out games, there are a few options
Unimpressive statlines, the inability to block, and returning to the battlefield tapped are all common traits, but none of these drawbacks interfere with the primary purpose of these cards
The only fast mana is Sol Ring, there are no infinite combos, and there is only one extra combat spell (Seize the Day)
And while I dont think itll see much play at all in any 60-card Constructed format, never say never