That's not the part that takes me significant time. The time consuming part (for me) is encounter design.
There are some quick & easy shortcuts. For instance, in 3e or 5e, a monster's CR is the level at which it's a default little speedbump encounter (that, in 3.5, might've killed someone) for a typical size party (in 4e, the monster would have to have the 'Solo' secondary role for that to hold true). No multiplier, no fussing. In 3e, if you wanted a larger combat, you 'broke up' the standard-issue lone monster into two CR = level -2 monsters. Neither doubling nor subtracting 2 were all that tough, though it could get troublesome if you wanted a bunch of different monsters of different CR. 4e to you total exp values of monsters, so long as they were within a few levels of the party, or you could use same-level monsters and just count up to the number of PCs. 5 PCs? 5 Standards or one Solo (worth 5) or an elite (worth 2) and three standards, etc, easy until you start varying monster levels. 5e, I find the general rule of thumb "don't outnumber the party" helps, just don't do it. Ever. For 5e? Same number of monsters, just double the exp and check the difficulty. Doubling's easy to remember & easy to do. Doubling also takes you from easy to medium or medium to deadly. Deadly is actually surprisingly reasonable if you're not doing many (or only 1) encounter that day, and the PCs aren't shy about cutting loose.
But, ultimately, tailoring encounters to a level and challenge is only one style of play - the other 'status quo' is to just place 'encounters' where they make sense for the setting and story, and let the players work out which ones are 'balanced' enough for them to take on (and always be ready to make adjustments).
This is why I personally have a huge preference for running canned modules in D&D - the last 3 editions place huge reliance on the combat subgame, but it is a lot of work to design robust balance encounters.
Between AL and two AP's a year, and 3pps, we have plenty of published adventures. As to the last 3 editions placing a lot of emphasis on combat, well, sure, they're like all the preceding editions, that way, and most older RPGs, for that matter - it was a criticism of RPGs in general, in the 80s & 90s, that no matter what they're supposed theme or emphasis, they devoted a lot of rules, page count, &c to combat. Because, really, you have to: combat is where PCs (and plot-important NPCs) get inconveniently killed, and also what any non-combat conflict always runs a risk of degenerating into - you need to get it working.