Though I do think they should definitely remove the one-summon limit. Changes from the base rules, when they're going to make them, should be:

1. Stuff that improves the core game - taking advantage of stuff you can do with a computer handling the rules. Limiting people to one summon makes things worse.

2. Stuff that is necessary because it can't be done without a DM to handle things. Obviously that's not the case here.

3. Stuff that doesn't break core, iconic D&D stuff. Limiting summons basically guts the entire concept and gameplay style of D&D summoners; summoning hordes is very much central to many iconic classes, builds, and spells.

4. Stuff that is intuitive or which makes the game more intuitive. The summon limit is awkward, game-y, and makes no in-universe sense.

Seriously this is an inexplicable change. Back in D:OS2 they argued it made the game easier to balance, but D&D is already balanced around having multiple summons, so in this case they broke the game's balance in order to make things less interesting and less fun, while losing an iconic part of the source material in the process. What an awful decision.